| Polymers with co-continuous structures exhibit application in various fields.The fabrication of them has attracted much attention.However,there are still some open problems.Firstly,it is very hard to prepare co-continuous structures in nanoscales because of the poor miscibility of components in their blend;secondly,the reported strategies(e.g.premade block copolymer as compatibilizers)for the fabrication of cocontinuous structures concern complicated processes,which is not suitable for the mass production.It is still a challenge to obtain the nanoscale co-continuous structures by reactive blending;finally,the basic understanding of formation mechanism of cocontinuous structures remains obscure.In this work,we propose a strategy to fabricate co-continuous structures by compatibilizing immiscible commercial polymer blend by taking PVDF/PLLA as an example by means of reactive comb compatibilizer(RCC).The formation mechanism and influence on the co-continuous composition windows have been systematically investigated.Then,the co-continuous structures from immiscible blend have been adopted as the template to prepare porous PVDF materials.1)Fabrication of nano-cocontinuous structures based on RCC: In the case of PVDF/PLLA(30/70)blend with extremely low volume/viscosity ratio,sub-100 nm cocontinuous structures have been fabricated successfully by RCC.The resultant materials exhibit better mechanical,lower haze and excellent thermal stability.The formation mechanism of the co-continuous structure was confirmed to be "sheet formation mechanism followed by sheet breakup to a network with extended structures".The existence of RCC produces the following influence.On one hand,RCC with double brushes stabilizes its location at the interface because of the stress balance.This is the reason for the reduced interface tension,higher interface fraction,and lower magnitude of the characteristic size;on the other hand,the PMMA backbones along immiscible interface and the repulsion effect of binary brushes result in the enlarged interface curvature radius,accounting for the occurrence of nanoscale co-continuous structures.Therefore,a new strategy of 100 nm co-continuous structure construction was successfully established.2)The processing sequence dependence of co-continuous structures: Three different methods(PVDF/RCC premixed,simultaneously mixed,PLLA/RCC premixed)have been adopted to investigate the processing sequences dependence of co-continuous structures.It was found that co-continuous structures have been obtained in all specimens.The sample of PLLA/RCC premixed exhibits the smallest characteristic size(~50nm),which can be attributed to the higher reaction probability between PLLA and RCC.As a result,this sample shows better mechanical properties and lower haze.3)Influence of RCC on the co-continuous composites window: A new method has been developed to validate co-continuous structures by combining solvent etching and morphological characterization.The results indicate that the addition of RCC widen the composition window of co-continuous structures(from 60/40 to 20/80-70/30).The existence of RCC produces the following influence.On one hand,it increases the viscosity of PLLA and decreases the interface tension;on the other hand,the balanced stress on two sides and the repulsion effect(resulted from immiscible PVDF and PLLA)of binary brushes are benefit to the improvement of interface curvature radius,which plays a key role in the formation of co-continuous structures.4)Fabrication of porous PVDF membranes based on the nano-cocontinous structures template: A new strategy to prepare porous materials based on cocontinuous structure template has been developed.As a result,porous PVDF membranes have been prepared by removing PLLA by means of selective solvent.It is facile to tailor pore structure/size and water flux by varying composition in PVDF/PLLA/RCC blend.The resultant PVDF porous material exhibits good mechanical properties. |
