氧化石墨烯对VS55冻融过程结晶行为的影响

Effects of graphene oxide on crystallization behavior of VS55 during cooling and warming

借助差示扫描量热仪(DSC)和低温显微系统,研究了升降温速率(5、10、25、50和100℃/min)和氧化石墨烯(GO)浓度(0.01、0.1、1和5 mg/ml)对VS55溶液降温过程结晶和升温过程冰晶再生长的影响。结果表明:(1)随着升降温速率的增加,VS55溶液体系在降温过程中的结晶焓Hf以及升温过程中的再结晶焓HTd都会减小;(2)对浓度为2.1 mol/L的VS55溶液进行降温时,GO浓度越大,其结晶焓Hf越大,且初始冻结温度显著提高;但对4.2 mol/L VS55降温时,其结晶焓Hf会随着GO浓度增加呈现出先减小后增大的特点;8.4 mol/L VS55已完全玻璃化,GO对其没有影响;(3)在升温过程中,GO浓度越高,VS55浓度越低,其溶液体系内冰晶再生长抑制程度越大,如GO浓度为5 mg/ml时,2.1 mol/L VS55溶液添加GO前后再结晶焓的差值ΔHTd为14.55 J/g,而4.2 mol/L VS55就显著降低到7.95 J/g,接近8.4 mol/L VS55的6.91 J/g。总体来看,GO对VS55溶液降温过程冰晶生长特点的影响主要取决于VS55浓度和GO浓度,但对复温过程反玻璃化或冰晶再生长特点的影响主要取决于VS55浓度、GO浓度以及升降温速率。

The effects of cooling and warming rates(5,10,25,50 and 100℃/min)as well as the concentration of graphene oxide(GO)(0.01,0.1,1 and 5 mg/ml)on the crystallization of VS55 were studied by differential scanning calorimetry(DSC)and Cryomicroscope during both cooling and warming process.The results showed that:(1)As cooling and warming rates rised,both the freezing crystallization enthalpy H f and the recrystallization enthalpy H Td became smaller.(2)For the case of cooling 2.1 mol/L VS55,the larger the concentration of GO,the more the crystallization of the 2.1 mol/L VS55 solution was,and the initial freezing temperature of the solution was increased obviously.For 4.2 mol/L VS55,however,the crystallization enthalpy H f presented a trend of first dropping then rising when increasing GO concentrations.And GO has little effect on both freezing crystallization during cooling and recrystallization during warming for 8.4 mol/L VS55.(3)For the cases of higher concentrations of GO as well as lower concentrations of VS55,the crystal growth inside VS55 was inhibited more significantly during warming.For example,when adding 5 mg/ml GO,the recrystallization enthalpy offrozen 2.1 mol/L VS55 reduced by 14.55 J/g,that of 4.2 mol/L VS55 reduced by 7.95 J/g,which was close to 6.91 J/g of 8.4 mol/L VS55.In general,GO and VS55 concentrations mainly affect the growth of ice crystals during the cooling process,but the main factors,which affects the devitrification or recrystallization during the rewarming process,include the concentration of VS55 and GO as well as the cooling and warming rates.