Investigation About The Electro-spinned Thermo-& Light-dual Responsive Copolymer Nanofilms Used For Smart Cleaning And Its Response Mechanism

As a kind of"active"material,stimuli-responsive polymers(SRPs)have been intensively investigated for decades.Among them,light-and thermal-responsive polymers play an important role in human's lives and works because of their broad applications,easy control and low cost.As a new type of textile material,intelligent textile has been rising rapidly in recent decades due to the strong demand of the market.In addition,it also fast combines with biology,chemistry,physics,electronics and other different fields.Our research group has sucessfully constructed intelligent textiles by combining stimulus-responsive polymers with textiles.By cross-linking acrylate or acrylamide based thermo-responsive polymers onto the cotton fabrics,the fabrics with single thermo-responsive property can be prepared.It possesses the functions of intelligent cleaning,comfort regulation and anti-bacterial adhesion.Besides that,by cross-linking the cotton fabrics with the thermo-responsive(acrylate or acrylamide)/light-responsive(azobenzene)copolymer,the fabrics with both ultraviolet light and temperature sensibilities are obtained.The trans-cis isomerization of azobenzene under UV irradiation improves the hydrophilicity and improved the cleaning performance.Based on the previous investigation,we further explore the effect of the azobenzene molar ratio in the copolymer to the cleaning capability.Besides that,the influence of the polymer chain orientation from the electrospinning process to the cleaning performance is also probed.Comparing to the cross-linked dual-responsive copolymer,the isomerization efficiency in the electronspinned copolymer is higher when the azophenyl groups are exposed to ultraviolet radiation.Thus,the cleaning capability of the intelligent textiles is further improved.(1)Synthesis and characterization of double responsive copolymers.First of all,the light-responsive monomer PAHA is obtained by a two-step substitution reaction and its UV responsive performance is studied.Then,it is copolymerised with the thermo-responsive monomer OEGMA₃₀₀ to obtain the dual-responsive copolymer.Among them,the copolymer P(OEGMA₃₀₀-co-PAHA)is prepared by ATRP approach.The monomer ratio of the product is 8(OEGMA₃₀₀)?1(PAHA),the transition temperature at ambient condition(TT_am)is 53?,whereas the transition tempertuare under UV irradiation(TT_UV)is shifted to a lower value(52.5?).The block copolymer POEGMA₃₀₀-b-PPAHA is prepared by RAFT approach.The monomer ratio of the synthesized product is 6(OEGMA₃₀₀)?1(PAHA).The glass transition temperature is-24?.TT is 50?.(2)Abnormal rapid water loss and rehydration behaviors of double-responsive copolymer films under ultraviolet radiation.In situ neutron reflectance(NR)is used to trace the dehydration and rehydration process of P(OEGMA₃₀₀-co-PAHA)films.The OEGMA₃₀₀ and PAHA components in P(OEGMA₃₀₀-co-PAHA)thin films are randomly distributed.In 23?(below TT),D₂O vapor,the swelling ratio of d/d_as-prepis 1.61±0.01 and the volume fraction of D₂O is 39.3±0.5%when the film reaches equilibrium.After exposure to UV radiation for 60 s,d/d_as-prep andj(D₂O)were significantly reduced to 1.00±0.01 and 13.4±0.5%,respectively.It is caused by the trans-cis isomerization of azophenyl groups which induces the breaking of the hydrogen bond between OEGMA₃₀₀ and D₂O molecules.The water loss process caused by the trans-cis isomerization is 100 times faster when comparing to the dehydration caused by the thermal stimulus.After the UV radiation is removed,the film immediately reabsorbs water molecules and swells.After 200 s,d/d_as-prep andj(D₂O)returned to the hydration state,which is also 30 times faster than the initial hydration process.At 60?(above TT),the thin P(OEGMA₃₀₀-co-PAHA)film switched to the collpased state.There is no significant change when exposure to UV irradiation.Therefore,UV-induced dehydration and rehydration are dependent on the existence of the hydrogen bonds.(3)In order to further improve the cleaning capability of smart textiles,POEGMA₃₀₀-b-PPAHA/polyvinylidene fluoride(PVDF)light-and thermo-dual responsive composite fiber films with different molar fractions are prepared by electrospinning.First of all,the structure and composition of the film are studied.The light-and thermo-responsive properties of the films are thoroughly investigated.With the increase of the amount of dual-responsive block copolymer,the spinnability of the electrospun fibers becomes worse and even stickiness occurres.At the same time,because of the low Tg of the synthesized dual responsive block copolymer,the mechanical properties of the prepared blends are worse than those of the pure PVDF films.The overall hydrophilicity of the electrospun fiber film is obviously better than that of the coated film.A pronounced change of the contact angle is observed after UV irradiation.It indicates the trans-cis isomerisation of the inner azophenyl group is more obvious.A reduction of approximately 73%of the fluorescence intensity is realized in the electospinned fibers after washing at 30? when comparing to the uncleaned fibers.It is a significant improvement of the intelligent cleaning to the dual responsive copolymer cross-linked on cotton fabrics.It can be attributed to the orientation of the polymer chains during the electrospinning,which profoundly enhance the trans-cis isomerization efficiency of the azophenyl group under UV irradition.