Soft Template-controlled Preparation Of Porous Low-density Polymer Materials And Their Functional Applications

Because of their advantages in finely tunable porosity/density,high surface area,and good mechanical strength,polymeric porous materials have attracted remarkable attention.Typically designed porous polymeric materials have been widely used in catalysis,adsorption/absorption,tissue engineering,smart materials,environmental science and sensing.Thus,development of the methods for the preparation of porous polymeric materials is of great significance.During the last 20 years,our group have synthesized a series of porous polymeric materials using typically designed gel-emulsions as template,which was first reported by our group.Compared with hard template,gel-emulsion is a type of soft template.Merits of gel-emulsion-based soft template lies in no need of template removal,easy for large-scale synthesis,eco-friendly,etc.Usually,gel-emulsion is a type of gelatinous soft materials,which is made up of stabilizer,continuous phase,and dispersed phase.For common gel-emulsions,fraction of the dispersed phase cannot be lower than 74%.Gel-emulsions of this kind often have typical bifoam structure,rheological properties and shear thixotropy feature.Stabilizer plays a critical role in gel-emulsion formation.Commonly used gel-emulsion stabilizers include surfactants and micro/nanoparticles.These stabilizers show drawbacks in large consumption,difficult to remove,easy to cause pollution,and phase inversion,which bring hinderance in porous materials synthesis.To avoid the disadvantage,our group introduced the idea of using low molecular mass gelators（LMMGs）in gel-emulsion synthesis.Studies reveal that LMMGs can be used as efficient gel-emulsion stabilizers,as they show favorable merits:1)much lower comsuption than commonly used stabilizer;2)fraction of the disperse phase can be much lower than 74%;3)constitution of the gel-emulsion system can be largely adjusted.Though LMMGs-based gel-emulsions are favorable in many aspects,they may encounter difficulties when large-scale synthesis is required,due to time consumed synthesis and relatively high expense.Therefore,efforts need to be taken to develop more favorable stabilizers that can satisfy the demand for porous materials synthesis.Based on literature study and our previous research,it is deduced that excellent ability of LMMGs in gel-emulsion synthesis should be aroused from the gelation of continuous phase.Generally,gelation of the organic phase（continuous phase）is a crucial step in LMMGs-based gel-emulsion preparation,which facilitate further entrapping of water drops into the gel network during vigorous shearing.Enlightened by this,we propose that if we could develop superb gel-emulsions with common stabilizer referring to LMMGs-based gel-emulsion preparation through optimization of recipe and gelation process.It is expected that the obtained gel-emulsion could own both features of LMMGs-based gel-emulsions and common gel-emulsions.Accordingly,this thesis presents several preferrable gel-emulsions,where a small amount of stabilizer is needed and fraction of the dispersed phase can be varied in a wide range.With the newly developed gel-emulsions,several porous polymeric materials have been prepared and they exhibit favorable performance in 3D printing,photo thermal conversion,or sensing substrate.Part one:New kinds of mechanically robust,porous polymeric materials with varied internal structures were produced using a newly designed water-in-oil（W/O）gel emulsion as a template.The density,internal structure,and mechanical properties of the porous materials can be easily and largely adjusted by varying the water content and the stabilizer（SiO2）amount in the relevant gel emulsions.Specifically,the density and compressive strength could be changed from 0.19 to 0.96 g·cm-3 and from a few MPa to more than 100 MPa,respectively.Importantly,the materials obtained demonstrated unusual low-frequency sound absorption properties.In addition,the gel emulsions created can be used as a new kind of 3D printable material,which allows polymerization after printing.In this way,complicated architectures can be produced.Part two:A series of aerogels was prepared through the polymerization of a new Span 80-based water-in-oil gel-emulsion with a high-water content.The internal structure and properties（mechanical strength and thermal conductivity）of the monoliths can be adjusted easily by varying the water content in the gel-emulsion templates.Under the optimized conditions,a hydrophobic aerogel with density of 0.035 g·cm-3 was obtained.The aerogel had a good mechanical strength and low thermal conductivity（0.032 W·m-1·K-1）.The aerogel was used to purify water polluted with organic/inorganic salts:oil could be removed from an oil/water mixture by using the aerogel as an absorbent,and inorganic salts could be removed by using an interfacial solar vapor generation system that included the aerogel as key components.Both the removal processes had a favorable efficiency,reusability,and stability.Furthermore,the low cost（0.43 USD per liter）and scalable preparation of the aerogels indicates great potential for their application in water purification.Part three:A new kind of polymeric aerogel was developed using gel-emulsion as template.The obtained aerogel and the subsequent carbonized aerogel show desirable optical,thermal,and wetting properties,laying solid foundation for efficient solar-driven interfacial evaporation.With utilization of the aerogels-based solar-driven evaporation system,a high-water production efficiency of 2.1 kg·h-1·m-2 under 1-sun illumination was realized.Meanwhile,electricity was also efficiently produced via the combination of the solar-driven evaporation system with a home-made thermoelectric conversion device.The output power of the system is～66 W/m2 under 4 kW/m2 solar illumination.Owing to the convenience in preparation,high performance in solar conversion and fast water transportation,the reported materials would provide new opportunities for solar energy utilization.Part four:Preparation of multiphase emulsions（W/O/W）using a typically synthesized polymer surfactant.Using one-step synthesis,we got a new type of polymer surfactant.With the surfactant,multiphase emulsion of W/O/W type is obtained.Highly porous particles with open pores were achieved through the polymerization of the emulsion.Furthermore,the porous particles were used as substrate to make fluorescent sensing films.Six fluorophores with varied emission features were chosen as sensing units and they were immobilized onto the porous particles via physical adsorption.Interestingly,fluorescence intensity of the fluorophores showed remarkable enhancement when immobilized onto the porous particles,owing to t restriction of aggregation-caused quenching effect.Photostability of the fluorophore also showed obvious increase after the loading.Base on the modified porous particles,fluorescent sensor array was built,which can be used to distinguish common volatile organic compounds（VOCs）,including alcohols,amins,alkanes,etc.