The Calorimetric Studies Of Sub-Rouse Dynamic Modes In Polymers

The transformation and relaxation of polymers is the frontier research field of soft condensed matter physics.Learnimg about the relaxation characteristics and motion laws of polymers can help people understand the relationship between their microstructure and macroscopic properties better and deeper.The glass-rubber transition region of amorphous polymers has always been a hot topic widely concerned by scholars,in which the research of sub-Rouse modes is extremely limited,and there have never been reports that find the experimental evidences of sub-Rouse in a thermaldynamical manner.Given that sub-Rouse modes could be enthalpy related or thermal related,we should observe some unusual behaviour in the glass-rubber transition profiles due to the involvement of the contribution from sub-Rouse dynamics.In this paper,the Differential Scanning Calorimeter(DSC)is used to perform the relevant thermodynamic analysis on the polyisobutylene(PIB)and polystyrene(PS)with a series of molecular weight(M_w),and then their relevant thermodynamic and dynamic parameters,such as,glass transition temperature(T_g),the fictive temperature(T_f),fragility(m)and the index of non-exponential(?)are obtained.The relationship between T_g,m value,?value and their molecular weight is investigated.It is found that the T_g of PIB and PS both increase firstly and then reached the plateau region with molecular weight increasing,in addition,by analyzing the experimental results,the correlation between T_g of PIB and its molecular weight is T_g=205.2–7404.4/M_w;the correlation between T_g of PS and its molecular weight is T_g=370.2–51361.1/M_w.Then their experimental values normalized glass transition width are obtained through the analysis of the experimental data of PIB and PS,while their calculated values of normalized glass transition width are acquired taking advantage of m value and?value.In order to further analyze the glass-rubber transition region,we did an extensive survey covering all types of relaxation techniques to obtain reliable values of m and?.Using the values of m and?of PIB and PS,we calculated the glass transition width,and found that the calculated values are different from the experimental ones,greatly contrasting with PS and molecular glass formers,where the consistency is held quite well.Furthermore,the calorimetric experimental values are wider than calculated ones.This implies that some other dynamics than the?-relaxation are involved in the glass transition of PIB,and it should be sub-Rouse modes,which increases the types of measurement techniques finding the evidence of existence of sub-Rouse mode,verifies the universality of sub-Rouse mode of polymers,and can make people understand the glass-rubber transition region of polymers and various motion mechanisms more profoundly.