Construction And Performance Of Thermo-Responsive Materials By Utilizing Surfactant Properties

Energy is costful,hence,energy conservation is a necessary choice for sustainable development.As the main component of social energy consumption,building energy conservation is the key of energy conservation.Smart windows compsed of stimuli-responsive materials can reversibly adjust the transmittance of light,thereby showing excellent value.Different from other types,thermo-responsive smart windows require no manual operation and external settings such as electric fields,and can passively response to the changes in ambient temperature,which has greater advantages in energy saving.There are two general response modes,namely,the response to the opaque state occurs at high or low temperature,respectively.The former can block part of the heat-carrying sunlight from entering the room at the hot noon,reducing the energy consumption of the temperature regulation system;the latter can shade indoor activities in the cold night to protect privacy.The parameters for evaluating whether a smart window material is excellent,include light modulation capability,response speed,stability,switch adjustability,and reproducibility.At present,smart window materials with superior comprehensive performance are of great value.In addition,the two modes have their own advantages and complement each other.However,it’s difficult to combine two modes for fabricating a thermo-responsive smart window that not only saves energy but also protects privacy.It’s worth to explore how to combine the two modes.Amphiphilic molecules,typically represented by surfactants,have both hydrophilic and hydrophobic constitutes,which a class of potential stimuli-responsive units due to their solubility changes relating to temperature.Among them,N-substituted acrylamide polymers have been widely applied to smart window,while other types such as surfactant have not been intensively studied as smart window materials.This paper mainly employs amphiphilic molecules as thermo-responsive units to construct thermo-responsive materials,and explores their potential application as smart window materials in building energy conservation and privacy protection,thus expanding the controllability of smart window and successfully constructing the smart windows that integrate two modes.Chapter 1 is Introduction.We described the background of gels and smart windows,the basic characteristics and applications of surfactants and N-substituted acrylamide polymers.The development history,parameters and construction strategies of thermo-responsive smart windows were introduced in detail,and the types of thermo-responsive smart windows were comprehensively listed.The Krafft point(Tk)and cloud point(Tc)of surfactants,the volume phase transition temperature(VPTT)of N-substituted acrylamide polymers were discussed detailedly.At last,we summarized the advantages of amphiphilic molecules as a response unit,and then revealed the idea,research content and significance of this thesis.In Chapter 2,a series of thermo-responsive gel materials prepared by polyacrylamide(PAAm)with ionic surfactants(sodium dodecyl sulfate,magnesium dodecyl sulfate,sodium dodecyl sulfate,etc.)in water and ethylene glycol(W-EG)mixed solvents as smart window materials were prepared,of which the Tk of an ionic surfactant determineed the phase transition point that could switch transparency and opacity of gel materials.The switching point of the gel material,i.e.,the Tk of ionic surfactant,serving as intelligent windows could be flexibly regulated over a large temperature range(6-75℃),accompanying with high predictability by changing surfactant and/or adjusting the ratio of W-EG solvents.The existence of surfactant micelles possessed hydrophobic environments for solubilizing ultraviolet absorbents in PAAm gels,thereby endowing the UV shielding ability.This work could provide a new platform for functional soft materials with smart responsiveness.In Chapter 3,we presented a new surfactant-based smart window material to achieve a transition from the transparent state to the opaque state both at lower and higher temperatures,thus maintaining transparence at an intermediate temperature range.A nonionic surfactant,poly(oxyethylene)monoalkyl ether(C12(EO)6),and a cationic surfactant,hexadecylpyridinium bromide(HPB),were used to switch in the transparency transition caused by a combination of two mechanisms:the cloud point(Tc)of C12(EO)6 and the Krafft point(Tk)of HPB.The decrease in the hydration of the EO headgroups in C12(EO)6 above Tc and the crystallization of HPB below Tk triggered the thermal-response to temperature.We achieved the combine of the two modes of thermos-responsive smart window.In Chapter 4,considering the dependence between the Tc and Tk in regulating the surfactant-based smart window in the previous work,we synthesized poly(N-isopropyl acrylamide)nanogels(PN)and synergistically combined it with hexadecylpyridinium bromide(HPB)to obtain a new opaque-transparent-opaque transition gel.By changing the comonomer to adjust the VPTT of the nanogel,and introducing inorganic salts to adjust the Tk of the HPB,a thermo-responsive smart window,of which transition point can be independently adjusted,is conventiently generated.In Chapter 5,we prepared an ionic liquid gel with high transmittance to near-infrared(NIR)light in a transparent state and high transparency switching,which was constructed by 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt([BMIm][NTf2],as the solvent),PN(as the responsive unit)and methyl methacrylate(MMA,as the polymerized monomer).Contrary to the change rule in water,PN was opaque at low temperature and transparent at high temperature in[BMIm][NTf2].The gel was appied to smart window,of which Tlum and ΔTsol were high to 98.7%and 78.7%respectively,realizing the efficient regulation of sunlight.