The Creation Of A Small Molecular Gelling Agent-stabilized Gel Emulsion And Its Application In The Synthesis Of Low-density Materials

Methods used for the preparation of porous materials could be classified into hard template method and soft template method.The hard template method can be employed to fabricate highly ordered porous materials,but it suffers from sacrifice of template,and thereby it may not be suitable for large-scale preparation.In contrast,soft template method,which includes mainly gel-emulsion template,draws widespread attention due to its convenience in the control of the pore structure and size,and the simplest in the preparation process.As it is known,gel-emulsions are two-phase systems,of which one is the internal or dispersed phase,and another is the continuous phase.Unlike coventional emulsions,gel-emulsions possess typical rheological properties of physical gels.Furthermore,for conventional gel-emulsions the volume fraction of the internal-phase should be exceeding 0.74.Surfactants and micro-/nano-particles are the most commonly found stabilizers of gel emulsions.The gel-emulsions stabilized by them generally suffer from larger dose and phase-inversion problems.Recently,my supervisor,professor Fang,and his colleagues introduced,for the first time,low-molecular mass gelators（LMMGs）as a novel class of stabilizers into gel-emulsions.It was found that some of the LMMGs or LMMGs-like compounds are powerful stabilizers,and the gel-emulsions created from them are more stable,laying foundation for them to find real-life applications.Moreover,the volume fraction of the internal phase of this kind of gel-emulsions needs not to be more than 74%.One of the reasons behind is that at this case the continuous phase is staying as a gel,which traps water within the system.Based upon literature research and previous work from our group,various new stabilizers were developed and used for the preparation of new kinds of gel emulsions and porous polymeric monoliths.Techniques,such as ¹HNMR,FTIR,rheological methods,SEM,TEM,XRD,XPS,etc.were employed to investigate the structures,the properties of the gel-emulsions as prepared.The wettability,the mechanical properties,and the internal structures of the materials as prepared were also characterized via utilization of various techniques.Moreover,preliminary tests were also conducted to look at the possible applications of the porous materials as obtained.Specifically,the following research has been done during the thesis work.Part one:Stabilizer（1）,which is a di-cholesteryl derivative with a ferrocenyl unit appended to its linker.This LMMGs-like compound is an efficient gelator for n-heptane,n-octane,n-nonane,and n-decane,and in addition it is also an efficient stabilizer for gel-emulsions,such as water/n-decane,water/t-BMA,water/MMA,and water/styrene.For the system of 1/water/n-decane,the maximum volume ratio of water（dispersed phase）in the system could be 98%（v/v）.Optical microscopy measurements confirmed the foam-like structure of the gel-emulsions.SEM observation and XRD analysis revealed that the gelator assembled in a similar way in its pure n-decane gel as it in water/n-decane gel-emulsion.Rheological measurements demonstrated that both the gel-emulsion and the gel possess good mechanical stability,and exhibit typical viscoelastic properties.Unlike conventional gel-emulsions,the LMMGs based gel-emulsions,at least the examples reported in this work,possess a number of superiors.For example,the content of the stabilizer in a gel-emulsion can be notably lower than that when conventional surfactant or micro-/nano-particles are used as stabilizers,and the preparation process could be very simple.No doubt,these characteristics must favor their practical applications.Furthermore,salt resistance property will be possessed by a gel-emulsion if a neutral LMMGs,as the one reported in this article,is adopted as a stabilizer.This will definitely add additional values to the applications of the gel-emulsions.Compound 1 has also been utilized as a stabilizer for preparation of some gel-emulsions of water in some monomers,and a porous polymeric monolith was successfully prepared by polymerization of the gel-emulsion of 1/water/t-BMA with divinylbenzene（DVB）as a cross-linker.Part two:A ferrocene derivative of bi-cholesterol,a typical LMMG,has been successfully used as a stabilizer to create a gel emulsion of water/t-BMA.Based upon this gel-emulsion,a porous polymeric monolith,and a number of relevant porous composite monoliths have been prepared via polymerization of the system or the system with suitable silanes in the continuous phase.It has been demonstrated that the internal structure and the macroscopic properties of the porous materials could be easily adjusted by simple variation of the composition of the gel emulsion.Furthermore,the porous composite monoliths are ideal sorbents for kerosene,a representative of less viscous oils,and already used transformer oil,a representative of viscous oils.The sorbents after sorption could be recovered by simple centrifugation or squeezing,washing and natural drying.Considering the fast sorption rate,the relatively large absorption capacity,the adaptability to less viscous oil and to viscous oil,as well as re-usability,it is safe to say that the present study has paved a way for the porous composite materials to find real-life uses.Moreover,the approach developed in the present work is simple,low-cost,versatile and environmentally benign,and thus showing a bright future for synthesizing advanced,in particular,ultra-low density materials with superior performances.Part three:A cholesteryl derivative,BuDphe,which is a typical LMMG,was synthesized and successfully used as a stabilizer for the creation of water in t-BMA gel-emulsion.Polymerization of the continuous phase,t-BMA,resulted in porous poly-t-BMA monolith with controllable internal structure and density.To improve the mechanical properties of the materials,PDMS and a silane were employed as modifiers to prepare porous hybrid polymeric monoliths.As expected,the hybrid monoliths as prepared possess not only hydrophobicity,porosity,and low-density,which are the characteristics of the pristine poly-t-BMA monolith,but also flexibility in dry state,which is a property rarely found for other porosity polymeric monoliths prepared in a gel-emulsion template method and is crucial for real-life uses due to its convenience in transportation and storage.Moreover,modification,in particular when silanes were used as modifiers,also improves the thermo-stability of porous materials.Absorption test demonstrated that the silane modified porous monolith（MO-5）can be used as an excellent absorbent for a number of commonly found organic solvents or oils.The materials after absorption are easy to be re-generated and the liquids absorbed can be collected by simple squeezing.Re-usability test with CH₂Cl₂ as an example solvent demonstrated that the monolith of MO-5 could be recycled at least 10 times with no significant reduction of its absorption capability.Therefore,it is believed that the gel-emulsion template method developed for the preparation of the porous hybrid monoliths is versatile and facile,and shows bright future for synthesizing advanced,in particular,porous low density materials with superior oil-water separation properties.Part Four:A simple metal compound,ferrocene formic acid,is chosen as stabilizer to generate gel emulsions.Stability of the resulting gel emulsions and the proper polymerization temperature are optimized by using an optical micro-rheometer.It is shown that the type and the amount of the monomers can not only affect the pore structure but also the size of the porous materials.Based upon this stabilizer,a mixture liquid of St:AN（styrene and acrylonitrile,1:1）and water were chosen as a continuous phase,and a dispersion phase,respectively,and polymerization of the system resulted in a porous polymeric monolith.Interestingly,the materials as produced in a larger scale are still possessing the structure and properties of the materials produced in much smaller scale.More interestingly,the materials not only possess good mechanical properties,but also can be mechanically processed,such as cutting into pieces.After carbonization in N₂ atmosphere,the sizes of the porous materials were shrunken,but the internal structures are remained.Further carbonization in air resulted a material with no further shrunken,but the composition of the materials was changed.For example,Fe₃O₄ in the further porous materials changed into Fe₂O₃.Accompanied this change,the material also changed from hydrophobic to hydrophilic.However,the superparamagnetic property of the Fe₃O₄-containing materials is remained after the further treatment.Preliminary test revealed that the hydrophilic porous materials are good adsorbent of Cd²⁺,which opens a possibility for the purification of waste water.Part five:A stable W/O gel-emulsion was created by employing a cholesteryl derivative,BuDphe,as a stabilizer,a functional silica（Si-NDI）as a co-stabilizer,AIBN as an initiator,DVB as a crosslinker,styrene as the continuous phase and water as the disperse phase.Polymerization of the gel-emulsion resulted in porous monolithic materials.The internal structures of the materials as produced could be further tuned by introducing Span-80 and toluene into the gel-emulsion system.In this way,three materials,Ms-1,Ms-2 and Ms-3,with different internal structures were prepared.Studies have shown that the obtained porous materials can serve as adsorbent of heavy metal ions.For the adsorption of known six metal ions,they follow the following order:Pb²⁺>Cd²⁺>Zn²⁺>Cu²⁺.In the adsorption of Pb²⁺ by the three materials,it was shown that the internal structures of the materials show great effect upon the adsorption.Furthermore,adsorption of Pb²⁺ quenches the fluorescence emission of the materials,implying visualization of the adsorption.Part six:A stable W/O gel-emulsion was created by employing a cholesteryl derivative,SiDpheC,as a stabilizer.During the preparation,St and DVB were employed as a monomer and a cross-linker,respectively,and they compose the continuous phase and water is functioning as the dispersed phase.Polymerization of the continuous phase resulted in a new kind of porous materials.Furthermore,the internal structures of the monoliths could be largely adjusted via simple variation of the compositions of the gel emulsions.The strengths of the monoliths can be improved by doping inorganic oxides within the materials.It was lucky to find that the strength of a composite porous material of a density of about 0.26 g/cm³ as prepared is close to that of high quality building bricks（6.4 MPa）.Part seven:In this section,gel emulsions are generated by using a new kind of stabilizers that are the staple fibers of aramid 1313 and 1414,which were pretreated by a strong inorganic acid.Porous polymeric monoliths were obtained by polymerization of the gel-emulsions.Different from former porous materials,the materials prepared from theses kind of new gel-emulsions possess much higher porosities,and the pores within them are well connected by throats.Moreover,the 1313-based gel emulsion exhibits excellent rheological property and high mechanical stability that makes it a suitable material for injection molding.Contact angle tests show that the materials are hydrophilic,suggesting they may have the potential to purify water because of their porous structures.