TEXTILES AND METHODS OF MANUFACTURE

STATEMENT REGARDING FEDERAL SPONSORED

RESEARCH ON DEVELOPMENT

This invention was made with government support under DEAR0000527 awarded by DOE ARPA-E. The government has certain rights in the invention.

REFERENCE TO THE RELATED PATENT APPLICATIONS

This Utility Patent Application is based on a Provisional Application No. 62/746,347 filed on 16 October 2018.

Mi l l) OF THE INVENTION

The present invention is directed to energy saving and environmentally responsive smart materials, and in particular, to production of composite textile materials capable of self- regulation of thermal exchange between a wearer’s body and the environment.

The present invention also addresses fabrication of smart textiles from bi-morph meta fibers capable of self-adjustment of the textile’s infrared emissivity to a heat/humidity comfort zone in response to environmental parameters fluctuations.

In overall concept, the subject invention addresses a smart textile fabricated from yams containing bi-morph meta fibers formed through spinning of two antagonistic polymer (hydrophobic and hydrophilic) components with optical nanostructures embedded at least in one polymer component, and heat training (setting) of the yarns in a predetermined heat/humidity diapazone to attain environmentally responsive properties through modulation of the electromagnetic coupling between the optical nanostructures in the fibers resulting in self- regulation of the heat transport in the smart textile to remain in the heat/humidity comfort zone. In addition, the present invention is directed to manufacturing of wearable garments from bi-morph meta fibers which are embedded with selected optical nanostructures incorporated in the fibers and demonstrating a dynamic humidity responsive behavior due to an effective electromagnetic coupling of the optical nanostructures self-adjustment.

The present invention also addresses a single-step spinning process for manufacturing a meta fiber-based material having a tunable infrared emissivity and heat transport adjustability in response to the environmental humidity fluctuations in order to maintain a wearer’s thermal comfort zone without external power consumption.

BACKGROUND OF THU INVENTION

Energy saving is an important issue for development of human society and civilization. In U.S., about 40% of the total energy produced is consumed by residential and commercial buildings. Approximately 37% of the consumed energy is spent for heating and/or cooling in order to maintain thermal comfort for the inhabitants in the buildings. Such consumption of energy for heating or cooling of vast spaces of buildings results in substantial energy waste that contributes to deleterious global climate changing.

In view of such issue, there is a vast commercial interest in developing wearable clothing technologies that can provide comfort zone for wearers of the clothing that would reduce a large amount of energy consumption for environment control in the buildings.

Usage of such clothing technologies can be even more beneficial in places other than residential or office buildings, such as, in severe working environments, for example, battle fields or hot and humid industrial settings. In these extreme settings, the regulation of the body temperature and heat transport through a wearer’s clothing would be extremely important for survival of people exposed to such severe environmental conditions.

Environmentally responsive textile materials for clothing can also be beneficial in an enhanced caring for infants and medical patients who require personal attendance to fulfill their thermal comfort needs. Bi-component fibers are fabricated with two antagonistic polymers having different chemical and/or physical properties. In the manufacturing process, the two polymers are extruded from the same spinneret with both polymers within the same filament.

A difference in shrinkage induced by the environmental stimuli , such as, for example, heat and/or humidity fluctuations, between the antagonistic polymers in the bi-component fibers results in a strong environmental response of the bi-component fibers.

Examples of the bi-component fiber based commercial products include Nike’s AeroReact™ and Mitsubishi Rayon’s Ventcool™ that use a perspiration responsive fabric designed to maintain a wearer’s skin dry by increasing air spaces in the textiles to promote sweat wicking. However, these technologies are neither capable of active regulation of the infrared radiation (which is the main thermal transport channel for heat dissipation from a human body to the environment), nor of active dynamic tunability of the infrared emissivity in order to self- regulate the heat transfer in response to environmental changes.

Infrared clothing is commercially available that incorporates nanoparticles to enhance the absorption of infrared radiation useful in hyperthermia therapy. However, the existing technology is a passive technology, and thus is not capable of self-regulation of the heat transfer through infrared radiation.

It would be highly desirable to further advance the fabrication of smart textiles from bi- component meta fibers capable of self-regulation of the heat transfer via active modulation of the infrared (IR) radiation and dynamic adjustment of the IR emissivity, as a channel of the heat transfer, to predetermined heat/humidity comfort zone responsive to the environmental deviation therefrom.

SUMMARY OF THU INVENTION

It is therefore an object of the present invention to provide composite materials manufactured from bi-component fibers with incorporated optical nanostructures that are configured with an optical coupling mechanism capable of an active tunability of the infrared emissivity responsive to the environmental changes. It is another object of the present invention to provide a smart textile capable of self- regulated thermal comfort for a wearer of the clothing made from the smart textile fabricated from bi-component meta fibers incorporated with optical nanostructures.

It is a further object of the present invention to fabricate smart textiles from bi-component (antagonistic polymer components) fibers, capable of dynamic mechanical changes due to the difference in moisture absorption by antagonistic polymers (one hydrophilic and the other hydrophobic), and demonstrating the actively tunable infrared emissivity resulting from the modulation in the electromagnetic coupling of the optical nanostructures embedded in the hydrophobic component of the fibers which is caused by the dynamically changing displacement of neighboring fibers with the purpose of maintaining the wearer’s comfort zone in changing environments.

It is an additional object of the present invention to provide a smart textile formed with composite fibers manufactured with at least two physically different base polymers and an optical nanostructure embedded therein to realize the meta-cooling textile (MCT) technology which would be capable of modulating the infrared emissivity of the textile in response to thermal discomfort, thus providing thermal regulation in a self-powered fashion (without the need for an extra power to maintain thermal comfort).

Furthermore, it is an object of the present invention to manufacture smart textiles with composite fibers capable of the dynamical tuning of the infrared radiation (as a primary channel for heat transfer through the textile) and of the energy exchange between the wearer’s body and the surrounding environment, thus providing efficient localized thermal management.

The present invention is also directed to the humidity responsive bi-component meta fibers fabricated from polymer composites having optical nanostructures incorporated therein, which, depending on the relative humidity and/or perspiration level, curls or straightens, thus modulating a relative disposition of optical nanostructures in the neighboring meta fibers to control the electromagnetic coupling between optical nanostructures in the neighboring meta fibers and to adjust the thermal radiation in the infrared range.

In addition, it is an object of the present invention to provide a composite fiber capable of a reversible self-regulation of a thermal transport mechanism, where the increase or decrease of the humidity level causes straightening or curling, respectively, of the meta fibers, that results in modulation of a relative displacement between the neighboring meta fibers, leading to enhanced or reduced infrared emissivity of the meta fibers, causing, in its turn, the adjustment of the heat transfer through the meta fibers.

It is a further object of the present invention to provide a melt spinning process for production of meta-cooling fibers, through the process steps, including: (a) pre-compounding of optical nanostructures into a hydrophobic polymer precursor, followed by (b) direct spinning of the hydrophobic polymer precursor with an antagonistic (hydrophilic) humidity responsive polymer precursor through a spinneret configured to form various configurations of bi- component meta fibers capable of a dynamic humidity response and self-regulated infrared emissivity.

It is also an object of the present invention to provide a heat“training” process to define an “open” state of the meta-cooling fibers under a wet condition, where the fibers are straightened to decrease the relative disposition of neighboring fibers to allow maximum electromagnetic coupling between optical nanostructures in the neighboring fibers, followed by the heat“training” step to define a“close” state of the meta-cooling fibers under dry condition, where the fibers are curled to increase the relative disposition of neighboring fibers to attain a minimum electromagnetic coupling between the optical nanostructures in the neighboring fibers.

It is a further object of the present invention to provide a scalable manufacturing process for production of meta-cooling fibers and textiles through the steps of: (a) compounding optical nanostructures with a polymer melt, (b) melt spinning of bi-component fibers, and (c) heat setting (training) to generate a dynamic humidity response of meta-cooling fibers.

It is still an object of the present invention to fabricate energy saving and environmentally responsive composite fibers for various applications, especially for on-body wearable humidity responsive clothing technologies, athletic apparel, medical and military clothing, as well as infant clothing, to attain an efficient and rapid self-cooling of the clothing, and for wearable technologies suitable in severe working environments capable of an effective self-regulation of thermal transport from a wearer’s body. In one aspect, the present invention addresses a smart textile fabricated from meta fibers. The meta fibers in the smart textile are fabricated as bi-component fibers configured with first and second antagonistic polymer components, one of which is a hydrophobic polymer component, while another is a hydrophilic polymer component. The hydrophobic and hydrophilic polymer components are combined in each bi-component fiber in either an eccentric sheath-core arrangement, or a side-by-side (key-lock) structural arrangement. In the eccentric sheath-core structure and arrangement, the hydrophilic polymer is used as a sheath, and the hydrophobic polymer is used as a core.

The base bi-component fiber further includes optical nanostructures dispersed in the hydrophobic polymer matrix for supporting the electromagnetic coupling between the optical nanostructures in the neighboring meta fibers. The electromagnetic coupling is determined by a distance (spacing) between the fibers, and determines the infrared emissivity of the composite fabric (smart textile).

In one embodiment, the subject bi-component meta fiber includes a humidity responsive mechanism ensured by the humidity responsive polymers.

The humidity responsive mechanism operates as follows:

(a) when relative humidity applied to the meta fibers is higher than a predetermined relative humidity level (also referred to herein as a comfort zone), the hydrophilic component of the meta fibers absorbs the moisture, causing the meta fibers to straighten. The meta fibers are arranged in yarns. When the fibers in each yarn are strengthened, the spacing between the neighboring fibers decreases which causes an increase in the electromagnetic coupling between the optical nanostructures, thus increasing the infrared emissivity and enhancing the heat transport due to the resonant electromagnetic coupling between the optical structures on the neighboring meta fibers;

(b) when, however, relative humidity applied to the meta fibers is lower than a predetermined relative humidity level (comfort zone), the hydrophilic component of the meta fibers releases the moisture, causing curling of the meta fibers, thus increasing their neighboring spacing within the yarn, thereby decreasing the infrared emissivity and reducing the heat transport. The optical nanostructures are embedded in the hydrophobic component of the meta fibers by compounding the optical nanostructures at a desired concentration prior to the spinning process. The optical nanostructures contemplated for inclusion into the subject meta fibers may include single-walled carbon nanotubes (CNT), double-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanohoms, carbon fibers, graphene, graphene oxides, carbon black, silver nanowires, copper nanowires, silicon nanowires, gold nanowires, gold nanoparticles, as well as their combinations.

The humidity responsive polymer contemplated for usage in the subject meta fibers may include Nylon 6, Nylon 66, cellulose, cotton, polyurethane, and their derivatives, as well as their combinations.

The hydrophobic polymer may include polyethylene, polyethylene terephthalate, polypropylene, polybutylene terephthalate, and derivatives thereof, and combinations thereof.

In another aspect, the present invention addresses a method of manufacturing a composite meta fiber material with self-regulated infrared emissivity responsive to the environmental humidity fluctuations, which comprises the steps of:

(a) compounding optical nanostructures into a hydrophobic polymer,

(b) forming a meta fiber by direct spinning of two antagonistic melt polymer components (hydrophilic polymer component and hydrophobic polymer component) through a bi-morph spinneret,

(c) arranging a plurality of the meta fibers into yarns, and

(d) heat setting (training) the meta fibers to an“open” state in a wet condition, and to a “close” state in a dry condition. When the trained meta fibers are exposed to fluctuating environmental conditions, the trained meta fibers, depending on the humidity deviation from a predetermined comfort zone, change their configuration, as“prescribed” by the heat training process, and thus modulate a spacing between the neighboring fibers. This changes the electromagnetic coupling between the optical nanostructures, and thus regulating the IR emissivity to control the heat transport between the wearer’s body and the environment.

These and other objects and advantages of the present system and method will be more apparent from reading the following Detailed Description of the subject invention in conjunction with the Patent Drawing figures. BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A - 1F are representative of the subject MCT fibers with self-regulated infrared emissivity illustrating a mechanism for an enhanced or a reduced heat transport at different humidity conditions, with FIGS. 1A and 1B showing a curved configuration and a strengthened configuration of the fibers, respectively, FIGS. 1C and 1D showing enlarged and reduced spacing between the fibers in the yam, respectively, and FIGS. 1E and 1F showing a textile formed from the fibers/yarns in the dry (reduced distance between yams) and wet (increased distance between yams), respectively;

FIG. 2 is a schematic representation of the subject direct bi-morph spinning system for production of the subject meta-cooling fibers;

FIGS. 3A - 3B are schematic diagrams of the subject system for spinning alternative configurations of the meta cooling fibers resulting in a side-by-side configuration (FIG. 3A) and an eccentric core-sheath configuration (FIG. 3B);

FIGS. 4A-4D are optical and SEM images of the cross section of the subject meta cooling fibers produced by the subject direct spinning process, with FIGS. 4 A and 4C being the optical and SEM images of the side-by-side meta cooling fibers, respectively, and FIGS. 4B and 4D being the optical and SEM images of the eccentric sheath-core meta cooling fibers, respectively;

FIGS. 5A-5D are SEM images of the subject meta cooling fibers with the eccentric sheath-core structure, where FIG. 5 A is a top view of the cross section of the subject meta cooling fiber with eccentric sheath-core structure, FIG. 5B is the enlarged image of the core area, FIG. 5C is the side view image of a split subject meta cooling fiber with eccentric sheath-core structure, and FIG. 5D is the enlarged side view image of the core area showing the uniform distribution of the embedded carbon nanotubes as the meta element;

FIG. 6 is a diagram representative of the Raman spectrum distribution of the core component of the subject meta cooling fibers in the core-sheath configuration;

FIG. 7 is a photograph of the collected bobbins of meta cooling yarns with different concentrations of carbon nanotubes incorporated (from left to right), with the carbon nanotube loading in the hydrophobic polymer component being 0, 100, 250, 500, 750, and 1000 ppm, respectively;

FIGS. 8 A - 8B are photographs of the knitted fabrics using the subject meta cooling yarns, with FIG. 8A being the photograph of the circular knitted MCT fabrics (from the top left to the bottom right, the carbon nanotube loading in the hydrophobic component being 0, 100, 250, 500, 750, and 1000 ppm, respectively), and FIG. 8B is the photograph of the double knitted MCT fabric with the PET fibers;

FIGS. 9A - 9B are the schematic diagrams representative of the mechanism for setting (training) of the set of the meta cooling fibers to define the“close” state in a dry condition for side-by-side structure (FIG. 9A) and the eccentric core-sheath structure (FIG. 9B);

FIGS. 10A - 10C are optical images of the subject meta cooling fibers showing the humidity responsive behavior after the heat setting step; and

FIG. 10D is a diagram representative of the yarn diameter vs. the relative humidity.

PET ATT, ED DESCRIPTION

The subject meta cooling fibers are envisioned as the foundation for energy saving and environmentally responsive garments fabricated from smart composite materials capable of actively maintaining a heat/humidity comfort zone for a wearer of such garment, where the heat transfer from a wearer’s body is self-regulated based on the infrared radiation changes in response to the environmental humidity fluctuations, as well as where a humidity response mechanism is implemented to maintain the clothes in the temperature/humidity comfort zone.

Referring to FIGS. 1 A - 1F, the subject meta fabrics 10 are arranged into yams 12, which are further knitted into the smart textile (fabric) 14.

The human body absorbs and loses heat primarily by the infrared radiation with the peak at -10 pm (Owen, M. S., 2009 Ashrae Handbook: Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.: 2009). The subject meta cooling fibers 10 forming the smart fabric 14 use the IR radiation-based heat transport mechanism for maintaining a thermal comfort zone for a wearer of a garment formed from the subject smart textile 14 by self-regulating the infrared emissivity in response to variations of the environmental humidity and /or perspiration level.

Optical nanostructures 16 are embedded in the meta fibers 10. The weight of the optical nanostructures 16 may fall in the range selected from a group of 0.0025-0.03%, 0.005-0.05%, and 0.01-0.5% of the weight of the hydrophobic component 30 in the meta fiber 10. The subject meta-cooling fibers 10 operate by modulating their infrared emissivity through changing the electromagnetic coupling between the optical nanostructures 16 embedded in the neighboring meta-cooling fibers 10 within each yam 12.

Referring to FIGS. 1A. 1C, and 1E, when the humidity in the environment is low (dry environment or low perspiration level), the meta fibers 10 curl (as shown in FIG. 1A), and thus attain a large fiber-to-fiber distance (spacing) 18, thus effectively reducing the electromagnetic coupling between optical nanostructures 16 in the neighboring meta fibers 10. The reduced electromagnetic coupling results in a small infrared radiation, i.e., reduced heat transport at the low humidity levels in the dry condition.

When the humidity in the environment increases, the meta fibers 10 straighten (as shown in FIGS. 1B, 1D, 1F) to decrease the fiber-to-fiber spacing 18 between the fibers 10 in each yarn 12 to match the human radiation peak (at 10 pm), thus increasing the resonant electromagnetic (EM) coupling between the optical nanostructures 16 in the neighboring meta-fibers 10, and thus maximizing the infrared emissivity, i.e., enhancing the heat transport at the elevated humidity levels/increased perspiration. Therefore, in response to the environmental humidity level fluctuations (dry, wet) or perspiration levels (low, high), the subject meta cooling fibers 10 are capable of self-regulating the heat transport by tuning the infrared emission from the subject textile 12 without the cost of an additional external energy usage. The subject humidity responsive self-regulation mechanism operates in a broad range of the predetermined relative humidity level, for example, from 5% to 90%, from 10% to 80%, or from 30% to 70%.

The scalable production of the subject meta-cooling fibers 10 is enabled first by a melt spinning process depicted in FIG. 2. As shown in FIG. 2, the system 20 for the subject spinning process includes a custom-designed bi-morph spinneret 32 which is uniquely designed (as will be detail further herein) and cooperates with a hydrophilic polymer feeder 22 containing a hydrophilic polymer melt 24, and a hydrophobic polymer feeder 26 filled with the hydrophobic polymer precursor 30.

The output 37 of the feeder 22 and the output 39 of the feeder 26 form the spinneret 32 and are used to extrude the hydrophilic polymer 24 and the hydrophobic polymer precursor 30, respectively, in a predetermined fashion to realize alternative meta fiber configurations. Optical nanostructures 16, which function to provide the optical coupling between the meta-cooling fibers 10, are pre-compounded into a hydrophobic polymer precursor 30 in the feeder 26 at a predetermined concentration.

The hydrophobic polymer precursor 30 containing the optical nanostructures 16 is subsequently spun together with the hydrophilic polymer precursor 24 at the bi-component spinneret 32 to form the bi-component meta cooling fibers 10, as shown in FIG.2. Subsequent to the formation of the bi-component fibers 10, they are arranged in yarns 12, which are wound on the yarn bobbin 21. The yarns 12 are capable of correlation of a spatial displacement between neighboring meta fibers 10 in each yarn through twisting, curling, self-crimping, texturizing, hot water treatment, water vapor heating, air flowing, and their combinations.

The bi-component spinneret 32 is capable of spinning the polymer precursors 24 and 30/18 in two configurations, including a side-by-side configuration 36 shown in FIG. 3 A, and an eccentric core-sheath configuration 38, shown in FIG. 3B.

In the exemplary embodiment shown in FIGS. 3 A - 3B, carbon nanotubes may be chosen as the optical nanostructures 16 to pre-compound into the hydrophobic polymer precursor 30. The melt polymer compound 24 and 30 can be disposed either side-by-side key-lock 36 (FIG. 3 A), or in the eccentric sheath-core structure 38 depending on which structure of the spinneret 32 is used.

As shown in FIG. 3A, in order to form the side-by-side configuration 36, the spinneret 32 is configured with the feeders 22, 26 having a side-by-side outputs 37, 39 from where the polymers 26, 30 are extruded in the side-by-side fashion to form the fiber configuration 36. Alternatively, as shown in FIG. 3B, the spinneret 32 is configured with the feeders 22, 26 arranged in a co-axial configuration having their outputs 37' in a surrounding relationship with the output 39' to extrude the polymers 26, 30 in the core-sheath arrangement 38. In the sheath-core structure 38, the optical nanostructures containing hydrophobic polymer 30 constitutes the core component 40 embedded within the hydrophilic polymer shell 42. This configuration 38 is beneficial in preventing the potential loss of the optical nanostructures 16 into the environment. The weight proportion of the core 40 may range, as an example, from 20% to 60% relative the sheath 42, or from 25% to 40% relative the sheath 42.

FIGS. 4 A - 4D depict the optical and SEM images of the cross-section of the exemplary embodiment, either in the side-by-side configuration 36 (in FIGS. 4A and 4C), or in the eccentric sheath-core configuration 38 (in FIGS. 4B and 4D). Although the diameter of the produced meta fibers in the example shown in FIGS. 4A - 4D range between 10 pm and 20 pm, the diameter of the meta fibers manufactured by the subject method may range in a broad diapason, for example, from 0.1 pm to 50 pm, or from 5 pm to 30 pm, or from 8 pm to 20 pm.

In order to examine the carbon nanotube doping as the meta element in the subject fibers 10, the eccentric sheath-core fibers 38 were micro-tomed and deliberately half-damaged to expose the core component 40 as shown in FIGS. 5 A - 5D. As best seen in FIGS. 5B and 5D, the carbon nanotubes (optical nanostructures) 16 are uniformly distributed in the core component 40. Such uniform distribution of the optical nanostructures 16 in the core component 40 proves that the melt spinning process does not negatively affect the incorporation of carbon nanotubes (CNTs). The Raman spectrum diagram, shown in FIG. 6, further confirms the successful embedding of CNTs 16 in the polyethylene core component 40 of the produced meta cooling fibers 10, exhibiting a characteristic G band at -1600 cm ¹ for CNTs.

FIG. 7 is a photograph of the produced meta cooling fibers 10 with an increased dosage (0, 100, 250, 500, 750, and 1000 ppm) of carbon nanotubes added (doped) in the hydrophobic polymer component. The color of the fibers changes (from left to right) from white to grey indicating the increasing dosage of the carbon nanotubes. Doping of the hydrophobic polymer component with carbon nanotubes does not interfere with the melt spinning process.

As an example shown in FIG. 8A, the fabricated meta cooling fibers can be exposed to a conventional fabric knitting process to produce either a single-jersey circular knitted fabric 14 (shown in FIG. 8 A), or a double-knitted fabric 14 (shown in FIG. 8B). Returning again to FIGS. 1B, 1D, 1F, after the spinning, the meta fibers 10 are arranged in the yams 12, and are set at a straightened configuration. To re-defme the“close” (or loose) state of the meta fibers at the dry conditions and the“open” (or tight) state of the meta fibers at the wet conditions, after the fiber spinning, a subsequent heat setting (training) step is performed at which the meta fibers 10, either in the side-by-side configuration 36 or in the eccentric configuration 38, are first exposed to a high humidity condition by immersing the fibers 10 into water. The fibers immersed into water, are mechanically twisted to define the“open” (or tight) state in the wet condition. Subsequently, as shown in FIGS. 9A - 9B, the fibers 10 in the original dry/low temperatures conditions are either bent into the curved structure 46 (FIG. 9A) or curled into a spring-like structure 48 (FIG. 9B), and thermally set to define the“close” (or loose) state in the dry condition. Thus trained, when the meta fibers are exposed to fluctuating environmental conditions, the meta fibers, depending on the humidity deviation from a predetermined comfort zone, change their configuration, as“prescribed” by the heat training process, and thus modulate a spacing between the neighboring fibers, resulting in changing the EM coupling between the optical nanostructures 16. The modulated EM coupling between the optical nanostructures 16 leads to the self- regulation of the IR emissivity to either decrease or to enhance the heat transport between the wearer’s body and the environment.

As shown in FIGS. 10A - 10C, a humidity responsive behavior is observed from a prototyped bimorph meta-cooling fibers 10 with an eccentric sheath-core structure arranged in a yarns 12, made of 70% : 30% Nylon 6 : polyethylene. In the prototype fiber, the polyethylene component (the core) of each fiber 10 was hydrophobic, while the Nylon 6 component (sheath) was hydrophilic. Two polymers are antagonistic components, i.e., they respond differently to the environmental humidity fluctuations, causing one of the materials to expand more than the other, thus transitioning the meta fibers between the“close” and the“open” states that are defined by the heat setting step (as illustrated in FIGS. 9A - 9B). Such humidity responsive behavior of the meta fibers 10 further modulates the relative disposition of neighboring meta fibers 10 in each yarn 12, thus controlling the infrared emissivity of the smart fabrics 14 containing the meta fibers 10.

When the environment is dry, the meta fibers curl to the“close” state to create a large distance (spacing) between each other, as shown in FIGS. 1A, 1C, 1E, 10A, and 10C, thus reducing the electromagnetic (EM) coupling between optical nanostructures in neighboring meta fibers 10. The reduction of the EM coupling between the optical nanostructures 16 in the meta fibers 10 results in a decreased heat transport through the infrared radiation. When the environment becomes wet, the meta fibers 10 straighten to the“open” state to reduce the distance therebetween, as shown in FIGS. 1B, 1D, 1F, and 10B, thus increasing the electromagnetic (EM) coupling between the optical nanostructures in the neighboring meta fibers 10, that results in the enhanced heat transport through the infrared radiation.

The relationship between the diameter of the yarns formed from the meta fibers and the relative humidity level is presented in FIG.10D.

The hydrophilic component may be a polymeric material selected from a group of: Nylons, Nylon 66, Nylon 6 (PA6), polyurethane, and their combinations.

The hydrophobic component may be a polymeric material selected from a group of Polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), and their combinations.

The optical nanostructures may be a nanomaterial selected from a group of single-walled carbon nanotubes, double-walled carbon nanotubes, few-walled carbon nanotubes, multi- walled carbon nanotubes, carbon nanohoms, carbon fibers, graphene, graphene oxides, carbon black, silver nanowires, copper nanowires, silicon nanowires, gold nanowires, gold nanoparticles, and their combinations.

EXPERIMENTAL RESULTS

Prototype meta fibers 10 have been fabricated by directly spinning two polymers 24, 30 into a bi-component structure having either the eccentric sheath-core configuration 38 or the side-by-side configuration 36, as shown in FIGS. 2 and 3A - 3B. One of the polymer precursor is the hydrophilic precursor 24 with the ability to absorb and desorb the moisture. This property of the hydrophilic material 24 results in the volume change and the relative distance change between neighboring meta fibers 10 in response to the humidity fluctuations. The other polymer 30, being hydrophobic, is the host for the optical nanostructures 16 uniformly embedded therein to enable the electromagnetic (EM) coupling between the neighboring meta fibers. In one of the implementations, CNTs are selected as the optical nanostructures that can be pre-compounded into the hydrophobic polymer 30 prior to the spinning. The CNTs have high electrical conductivity, chemical stability, mechanical flexibility, and textile fiber-matched length scales, and thus are good candidates for incorporation into the subject fibers 10.

In the experiments illustrated, the bi-component meta fibers 10 were spun through a custom-made spinneret 32 using Nylon 6 as the hydrophilic component and polyethylene as the hydrophobic component. Nylon 6 was selected because of its ability to absorb moisture, while polyethylene was selected due to its low absorption in the infrared range. The incorporation of CNTs in the polyethylene component did not interfere with the spinning process, as was confirmed at the optical and SEM images, shown in FIGS. 4A - 4D. Additionally, the CNTs remained uniformly distributed in polyethylene, was evident from the SEM images of the core area of an eccentric sheath-core meta fiber (FIGS. 5A - 5D), which was further confirmed by the Raman scattering spectrum showing the characteristic G band at -1600 cm ¹ for CNTs (depicted in FIG. 6).

As an example, meta cooling fibers 10 with the eccentric sheath-core structure and various dosages of CNTs in the core component (for example, 0, 100, 250, 500, 750, and 1000 ppm) were configured into yams 12 with a drawing ratio of 3.5: 1 and filament number of 288. The denier (unit of measurement used to determine the fiber thickness) of the produced meta fibers was changed from 1.0 to 2.1 depending on the ratio of the Nylon 6 and the polyethylene, as well as the rate of the spinning pump 34 (shown in FIG. 2). The color change of the meta fibers from white to gray (as shown in FIG. 7) indicates the increasing CNT dosage in the fiber.

The produced meta fibers 10 were arranged in the yarns 12, and subsequently the yarns were knitted into the textile 14 with either single jersey circular knitted structure (shown in FIG. 8A) or double knitted structure (shown in FIG. 8B) with polyester fibers as the supporting base. After the spinning, the meta fibers 10 within the yam 12 were correlated mechanically to attain the straightened configuration. Various CNT dosages (ranging from 0 to 1000 ppm) were embedded in the core polymer component. The produced meta fibers were strong enough to withstand the knitting process, indicating that the mechanical strength of the meta fibers was not reduced by adding the CNTs. To provide the self-regulation of the infrared emission in the meta fibers to result in the active modulation of heat transfer from the human body (garment wearer) to the environment in response to humidity level fluctuations, two states of meta fibers were defined:

(a) a“close” state where the meta fibers are loosely correlated to form a large relative distance (spacing) between the fibers 10 within each yam 12, as shown in FIGS. 1 A, 1C, 1D; and

(b) an“open” state where the meta fibers are tightly correlated to form a small relative distance (spacing) 18 between the fibers 10 within the yam 12, as shown in FIGS. 1B, 1D, 1F.

In the “close” state of the meta fibers, the electromagnetic coupling between the neighboring meta fibers is minimized, due to an increased distance 18 between the fibers 10. This configuration results in a reduced heat transfer from a wearer’s body to the environment, which is beneficial in a dry and/or cold situation.

To the contrary, in the“open” state of the meta fibers, the electromagnetic coupling between the neighboring meta fibers 10 is maximized due to a smaller fiber-to-fiber distance 18 (matching the infrared radiation wavelength), thus resulting in an enhanced heat transfer from the wearer’s body to the environment, which is beneficial in a wet and/or hot condition.

To“train” the fibers, i.e., to define the“close” state of the meta fibers at the dry (and/or cold) condition and the“open” state of the meta fibers at the wet (and/or hot) condition, a subsequent heat setting step is performed, as illustrated in FIGS. 9A - 9B. Specifically, after the spinning step, the meta fibers 10 were first twisted in water to define the“open” state in the wet condition, so that they could be either bent into a curved configuration 44 or curled into a spring like configuration 48, shown in FIGS. 9A and 9B, respectively. The fibers also were heat-set to define the“close” state in the dry condition (without water). The“close” state of said meta fiber was established by heat setting the meta fiber in a dry condition with the relative humidity level lower than 20%, and with heat setting temperature ranging between 80°C and 200°C.

In an exemplified demonstration, 72-filament meta yams using Nylon 6 and polyethylene with eccentric sheath-core structure were treated (trained) to establish the“open” and“close” states. After the treatment (training), the meta yams 12 demonstrated a large yarn diameter being exposed to a low humidity of 5%, but shrank to a smaller yarn diameter when the humidity was increased to 80%. Specifically, the functionality of the subject meta fibers is sufficient at predetermined relative humidity levels ranging from 5% to 90%, from 10% to 80%, and from 30% to 70%. The yarn diameter fluctuations though contracting or expanding of the yams responsive to the humidity level variations, and/or due to the sweat, is reversible with multiple humidity change cycles, proving a dynamic actuation of the produced meta fibers.

Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention as defined in the appended claims. For example, functionally equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular locations of elements, steps, or processes may be reversed or interposed, all without departing from the spirit or scope of the invention as defined in the appended claims.