The crystallization behavior of silica-filled polydimethylsiloxane(PDMS)was investigated in detail by^(1)H solid-state nuclear magnetic resonance(^(1)H SS-NMR)in combination with synchrotron radiation wide-angle X-ray...The crystallization behavior of silica-filled polydimethylsiloxane(PDMS)was investigated in detail by^(1)H solid-state nuclear magnetic resonance(^(1)H SS-NMR)in combination with synchrotron radiation wide-angle X-ray scattering(WAXS),and temperature-modulated differential scanning calorimetry(TMDSC)techniques.For neat PDMS,no apparent difference is observed for the crystallinity characterized by^(1)H SS-NMR and WAXS at low-temperature regions.However,upon filler addition,a 15%-35%lower difference in crystallinity is observed measured by^(1)H SS-NMR compared to WAXS.The origin of such mismatch was explored through multi-component structural,dynamics,and chain-order analysis of PDMS samples with different filler fractions.The 1D integrated WAXS results of PDMS with different filler fractions at different temperatures show that the packing structure as well as crystal size basically remain unchanged,but as the filler fraction increases from 0 phr to 60 phr,the rigid component’s dynamics order parameter S_(r)obtained by^(1)H SS-NMR decreases from 0.70 to 0.55.The filler fraction-dependent crystallinity calculated based on S_(r)was compared with experimental values,revealing a behavior of decreasing order in the crystalline region.Combining with the results of accelerated chain dynamics in crystalline region as reflected by T_(2)values,the molecular origin is attributed to the formation of CONDIS crystals,whose conformational order is lost but the position and orientation orders are kept.Such hypothesis is further supported by the TMDSC results,where,as the filler fraction increases from 0 phr to 60 phr,the melting range widens from 8.77 K to 14.56 K,representing a growth of166%.In addition to previous reports related to the condition for forming CONDIS mesophase,i.e.,temperature,pressure,and stretching,the nano-sized filler could also introduce the local conformational disorder for chain packing.展开更多
The general development of Rheo-NMR during the last four decades as well as selective hyphenated apparatuses is presented.Based on different magnet types,the current review is divided into two categories,namely low-fi...The general development of Rheo-NMR during the last four decades as well as selective hyphenated apparatuses is presented.Based on different magnet types,the current review is divided into two categories,namely low-field and high-field NMR,while the timedomain NMR is normally applied in the former case and the frequency-domain NMR is adopted in the latter one.Depending on different rheometer cells,it can be further divided into tensile and shear mode Rheo-NMR.The combination of various rheometer cells and NMR facility guarantees our acquisition of molecular level structure and dynamics information under flow conditions,which is crucial for our understanding of the molecular origin of complex fluids.A personal perspective is also presented at last to highlight possible development in this direction.展开更多
基金financially supported by NSAF Joint Fund of China(No.U2030203)the National Natural Science Foundation of China(Nos.51973207 and 51903230)。
文摘The crystallization behavior of silica-filled polydimethylsiloxane(PDMS)was investigated in detail by^(1)H solid-state nuclear magnetic resonance(^(1)H SS-NMR)in combination with synchrotron radiation wide-angle X-ray scattering(WAXS),and temperature-modulated differential scanning calorimetry(TMDSC)techniques.For neat PDMS,no apparent difference is observed for the crystallinity characterized by^(1)H SS-NMR and WAXS at low-temperature regions.However,upon filler addition,a 15%-35%lower difference in crystallinity is observed measured by^(1)H SS-NMR compared to WAXS.The origin of such mismatch was explored through multi-component structural,dynamics,and chain-order analysis of PDMS samples with different filler fractions.The 1D integrated WAXS results of PDMS with different filler fractions at different temperatures show that the packing structure as well as crystal size basically remain unchanged,but as the filler fraction increases from 0 phr to 60 phr,the rigid component’s dynamics order parameter S_(r)obtained by^(1)H SS-NMR decreases from 0.70 to 0.55.The filler fraction-dependent crystallinity calculated based on S_(r)was compared with experimental values,revealing a behavior of decreasing order in the crystalline region.Combining with the results of accelerated chain dynamics in crystalline region as reflected by T_(2)values,the molecular origin is attributed to the formation of CONDIS crystals,whose conformational order is lost but the position and orientation orders are kept.Such hypothesis is further supported by the TMDSC results,where,as the filler fraction increases from 0 phr to 60 phr,the melting range widens from 8.77 K to 14.56 K,representing a growth of166%.In addition to previous reports related to the condition for forming CONDIS mesophase,i.e.,temperature,pressure,and stretching,the nano-sized filler could also introduce the local conformational disorder for chain packing.
基金This work was financially supported by the National Natural Science Foundation of China(U20A20256,51973207)the NSAF Joint Fund(U2030203).
文摘The general development of Rheo-NMR during the last four decades as well as selective hyphenated apparatuses is presented.Based on different magnet types,the current review is divided into two categories,namely low-field and high-field NMR,while the timedomain NMR is normally applied in the former case and the frequency-domain NMR is adopted in the latter one.Depending on different rheometer cells,it can be further divided into tensile and shear mode Rheo-NMR.The combination of various rheometer cells and NMR facility guarantees our acquisition of molecular level structure and dynamics information under flow conditions,which is crucial for our understanding of the molecular origin of complex fluids.A personal perspective is also presented at last to highlight possible development in this direction.
