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1、DSC课件2023/2/2【可编辑】差示扫描量热仪差示扫描量热仪(DSC)nDSC测量样品吸热和放热与温度或时间的关系测量样品吸热和放热与温度或时间的关系吸热吸热 热流入样品，即样品吸收外界热量，为负值。放热放热 热流出样品，即样品对外界放出热量，为正值。国际标准国际标准ISO 11357-1:：DSC就是测量在程序控制温度下，输入到试样和参比物之间就是测量在程序控制温度下，输入到试样和参比物之间的的功率差（功率差（dH/dt）与与温度温度(T)的关系的一种技术。的关系的一种技术。该热流差能反映样品随温度或时间变化所发生的焓变：样品该热流差能反映样品随温度或时间变化所发生的焓变：样品吸收能量时
2、，焓变为吸热；当样品释放能量时，焓变为放热。吸收能量时，焓变为吸热；当样品释放能量时，焓变为放热。Endothermic Heat FlowlHeat flows into the sample as a result of either lHeat capacity(heating)lGlass Transition(Tg)lMeltinglEvaporationlOther endothermic processesEndothermicExothermic Heat FlowlHeat flows out of the sample as a result of either lHeat
3、 capacity(cooling)lCrystallizationlCuringlOxidationlOther exothermic processesExothermicDSC与与DTA测定原理的不同测定原理的不同lDSCDSC是在控制温度变化情况下，以温度（或时是在控制温度变化情况下，以温度（或时间）为横坐标，以样品与参比物间温差为零所间）为横坐标，以样品与参比物间温差为零所需供给的热量为纵坐标所得的扫描曲线。需供给的热量为纵坐标所得的扫描曲线。lDTADTA是测量是测量 T-T T-T 的关系，而的关系，而DSCDSC是保持是保持 T=T=0 0，测定测定 H-T H-T 的关系。两
4、者最大的差别是的关系。两者最大的差别是DTADTA只能定性或半定量，而只能定性或半定量，而DSCDSC的结果可用于定量的结果可用于定量分析。分析。热流型热流型(Heat Flux)(Heat Flux)在给予样品和参比品在给予样品和参比品相同的功率下，测定样品和参比品两端的相同的功率下，测定样品和参比品两端的温差温差 T T，然后根据热流方程，将然后根据热流方程，将 T T（温差）换算成（温差）换算成 Q Q（热量（热量差）作为信号的输出。差）作为信号的输出。功率补偿型功率补偿型(Power Compensation)(Power Compensation)在样品和参比品始终在样品和参比品始终
5、保持相同温度的条件下，测定为满足此条保持相同温度的条件下，测定为满足此条件样品和参比品两端所需的能量差件样品和参比品两端所需的能量差，并直接作为信号，并直接作为信号 Q Q（热量（热量差）差）输出。输出。调制热流型调制热流型(Modulated Heat Flux)(Modulated Heat Flux)在传统热流型在传统热流型DSCDSC线性变温基础上，叠加一个正弦震荡温度程序，线性变温基础上，叠加一个正弦震荡温度程序，最后效果是可随热容变化同时测量热流量，利用傅立叶变换将最后效果是可随热容变化同时测量热流量，利用傅立叶变换将热流量即时分解成热容成分动力学成分。热流量即时分解成热容成分动力
6、学成分。1、DSC的基本原理的基本原理FurnaceThermocouplesSampleReferencePlatinum AlloyPRT SensorPlatinumResistance HeaterHeat Sink热流型热流型 DSC功率补偿型功率补偿型 DSCSample传统量热仪内部示意图传统量热仪内部示意图精确的温度控制和测量精确的温度控制和测量更快的响应时间和冷却速度更快的响应时间和冷却速度高分辨率高分辨率基线稳定基线稳定高灵敏度高灵敏度 热流热流DSC 炉子剖面图炉子剖面图Dynamic Sample ChamberReference PanSample PanLidGas
7、 Purge InletChromel DiscHeating BlockChromel DiscAlumel WireChromel WireThermocouple JunctionThermoelectric Disc(Constantan)热流式热流式 DSC-工作原理工作原理RsRrTfsTrsTsTr热流式热流式 DSC-工作原理工作原理假设假设:1,1,传感器绝对对称，传感器绝对对称，Tfs=TfrTfs=Tfr，Rs=Rr=R Rs=Rr=R2,2,样品和参比端的热容相等样品和参比端的热容相等Cpr-CpsCpr-Cps3,3,样品和参比的加热速率永远相同样品和参比的加热速率永
8、远相同4,4,样品盘及参比盘的质量（热容）相等样品盘及参比盘的质量（热容）相等5,5,样品盘、参比盘与传感器之间没有热阻或热样品盘、参比盘与传感器之间没有热阻或热 阻相等阻相等 Heat Flux DSC:Theoretical DT MeasurementTrTsDTToTpTr=Reference TemperatureTs=Sample TemperatureTo=Onset of MeltTp=Peak of MeltTheoretically:To=TpTimeTemperatureActual Heat Flux DataSlope due to thermal lagDTViol
9、ations of AssumptionsPan and calorimeter heat capacities are ignoredSample and reference heat capacities are assumed to be the same and to heat at the same rate.In general the sample and reference calorimeter heat capacities do not match contributing to non-zero empty DSC heat flow rate baseline.Dur
10、ing transitions and MDSC experiments the sample and reference heating rates differ and the measured heat flow rate is incorrect because the sample and reference sensor and pan heat capacities store or release heat at different rates.Expanded Principle of Operation Q=Ts-Tr +A +B +C R ThermalResistanc
11、e Imbalance ThermalCapacitance Imbalance Heating RateImbalanceTfsTsRsTfrTrRrCsCrNot Being Measured w/Conventional DSCQ-Series DSC SchematicSample&Reference PlatformsTzero ThermocoupleQ-Series Heat Flow MeasurementTrTsRsCsCrRrToTfQ-Series DSCThe Tzero thermocouple provides anobjective reference point
12、 so that thosefactors previously assumed can be directlymeasured.Tzero Heat Flow MeasurementHeat Flow Rate EquationsHeat FlowSensor ModelThe sample and reference calorimeter thermal resistances and heat capacities obtained from Tzero calibration are used in the heat flow rate measurements.Differenti
13、al TemperaturesTzero Heat Flow Term ContributionslPrincipal heat flow provides main heat flow signallThermal resistance and heat capacity imbalance terms improve baselinelHeating rate difference term improves resolution and MDSC performanceTo技术的四相 热流方程基本热流基本热流热阻不平衡热阻不平衡热容不平衡热容不平衡加热速率不平衡加热速率不平衡标准DSC的
14、单项热流方程To技术提供的额外项T0及高级及高级T0技术对技术对DSC测量的改进：测量的改进：T0不需假设（不需假设（Q200/Q100 DSC):1,传感器绝对对称，传感器绝对对称，Tfs=Tfr，Rs=Rr=R2,样品和参比端的热容相等样品和参比端的热容相等Cpr-Cps3,样品和参比的加热速率永远相同样品和参比的加热速率永远相同高级高级To不需假设不需假设(Q2000/Q1000 DSC)：4,样品盘及参比盘的质量（热容）性等样品盘及参比盘的质量（热容）性等5,样品盘、参比比盘与传感器之间没有热阻或热阻相等样品盘、参比比盘与传感器之间没有热阻或热阻相等 Baseline Bow Impr
15、ovementSuperior Resolution on a Pharmaceutical Sample AnalysisAdvanced Tzero ResultsMDSC 测量什么测量什么?lMDSC 将热流分解成与变化的升温速率相关和不相关的两部分lMDSC将变化的升温速率叠加在线性的升温速率上是为了测量与变化的升温速率相关的热流 l一般来讲,只有热容与熔融的变化与变化的升温速率相关.lMDSC 的可逆和不可逆信号 绝不能 样品可逆和不可逆性质的测量MDSC 原理原理lMDSC 同时采用两种升温速率l平均升温速率l提供平均升温速率，它相当与普通标准 DSC 在同样升温速率下的信号l调制
16、升温速率l目的是为了在得到热流信号的同时得到热容的信号平均平均&调制温度信号调制温度信号调制温度平均温度Modulate+/-0.42 C every 40 secondsRamp 4.00 C/min to 290.00 C525456586062Modulated Temperature(C)525456586062Temperature(C)13.013.514.014.515.0Time(min)平均平均&调制升温速率调制升温速率周期平均升温速率调制升温速率0246810Deriv.Modulated Temperature(C/min)0246810Deriv.Temperature
17、(C/min)13.013.514.014.515.0Time(min)MDSC Raw Data SignalsModulated Heat Flow and Modulated Temperature(Heating Rate)Signals have an“Average”and an Signals have an“Average”and an“Amplitude”“Amplitude”调制DSC总热流：调制热流的傅立叶转换Calculation of Reversing CpModulated Heating RateModulated Heat FlowReversing Cp调制
18、DSC 不同成分的概念lMDSC Data Signals可逆热流Reversing Transitions热容Heat Capacity玻璃化转变Glass Transition大部分的熔融Most Melting 总热流 =可逆热流 +不可逆热流lMDSC Data Signals 总热流 =可逆热流 +不可逆热流不可逆转变热焓松弛Enthalpic Recovery挥发Evaporation结晶Crystallization热固化Thermoset Cure蛋白质变性Protein Denaturation淀粉糊化Starch Gelatinization分解Decomposition部
19、分熔融Some Melting调制DSC 不同成分的概念MDSC 无定形无定形 PETNonreversingReversingTotal-0.4-0.20.0Nonrev Heat Flow(W/g)-0.4-0.20.00.20.4Rev Heat Flow(W/g)-0.4-0.20.00.2Heat Flow(W/g)050100150200250300Temperature(C)Exo Up何时何时&为什么运行为什么运行 MDSC？l我需要比热信息吗？我需要比热信息吗？l转变是一个比热相关的现象吗转变是一个比热相关的现象吗?l有被其他效应掩盖的现象吗？有被其他效应掩盖的现象吗？l存在
20、对于标准存在对于标准DSC来讲很微弱或很宽的转变吗来讲很微弱或很宽的转变吗？l是否需要更高的灵敏度或分辨率吗？是否需要更高的灵敏度或分辨率吗？l比热会在恒温条件下随着时间而变化吗（比如比热会在恒温条件下随着时间而变化吗（比如恒温固化）？恒温固化）？何时何时&为什么运行为什么运行 MDSC？l对于熔融和结晶 l如果熔融过程看起来正常(单个吸热峰)并且在加热时无明显的结晶，就不必采用 MDSCl然而,如果熔融过程很复杂,或很难确定样品是否在加热时 存在结晶,采用MDSC l如果想得到比热(Cp)运行MDSCl通过常规DSC得到比热(Q1000 由于直接比热的测量是个例外)l采用较高的升温速率,10
21、C/minl需要三个实验基线参考样(蓝宝石)样品普通普通 DSC的局限性的局限性1.不可能在单个DSC的实验中同时提高灵敏度和分辨率升温速率快，灵敏度提高，分辨率下降升温速率慢，分辨率提高，灵敏度下降MDSC 可以解决该问题是因为他有两个升温速率2.基线弯曲度和漂移限制了DSC检测弱转变的灵敏度MDSC 消除了基线弯曲度和漂移是在于热容信号的取得是采用如下等式:K x 调制升温速率振幅调制热流振幅Cp=平均升温速率 x Cp可逆热流=3.图谱很难解释l因为DSC测量的是总热流lMDSC 不仅仅提供总热流，而且包括热容的信号和动力学组分4.很难通过普通DSC准确测量聚合物的结晶度.l准确测量结晶
22、度，需要:l确定真正的热容基线l定量测量在加热过程中有多少结晶在继续发展Application Heat Capacity Glass TransitionMelting and CrystallizationThermoplastics ThermosetsAdditional Applications Examples如果我们要用DSC测量比热怎么办？当f(x)=0 时（没有动力学相关现象时）。样品热流可简写为：Q=Cp m。通过两次不同加热速率对样品进行测试即可得到：K为仪器校正系数1、Cp的测量传统DSC测量样品比热Cp首先需要确定K值。可以通过已知比热的标准材料（如蓝宝石）来确定。基
23、线的重现性对Cp测量影响必须考虑。为了得到更好的Cp数据首先要测试空白基线，然后对每次样品 测试结果进行基线扣除。不要忘记我们在进行热流计算时的假设条件。这是测量误差的来源之一。K为仪器校正系数传统传统 DSC 测量比热的方法测量比热的方法:Effect of Side Chains on CpPolymerSide ChainCp(J/g/C)PE-H2.763PP-CH2.752PS-Ph2.139As the steric bulk of the side chain increases,molecular mobility decreases resulting in lower sp
24、ecific heat.B.Wunderlich,ATHAS Cp Data Bank,1985.Effect of Polymer Backbone on Cp#of MethylenesCp(J/g/C)10.622620.691830.708840.759780.7736OCH2n)O(As the number of methylenes increase,mobility isincreased in the polymer,resulting in higher heat capacity.B.Wunderlich,ATHAS Cp Data Bank,1985.Polyoxyal
25、kenes -153CEffect of Copolymer Composition on CpCompositionCopolymerCp(%PP)(Type)(J/C/mol)6.0block15.127.5random16.3915.5random18.54As PP concentration is increased,the number of methylenesincreases,resulting in a rise in specific heat capacity.Also,with randomness comes entropy（熵）,increase in mobil
26、ity,and increasein specific heat capacity.B.Wunderlich,ATHAS Cp Data Bank,1985.PE/PP Copolymer -93C2 Glass Transitiond Q/dtd Q/dt温度温度温度温度TgTg 1/2 从从DSC曲线上确定曲线上确定Tg的方法的方法PMMA 1st HeatPMMA-Aged1st Heat 10C/min6.87 mgEnthalpic Recovery Peak122.42C(H)-0.6-0.4-0.20.0Heat Flow(W/g)406080100120140160Temper
27、ature(C)Exo UpUniversal V4.2D TA InstrumentsPMMA 2nd HeatPMMA-Aged2nd Heat 10C/min6.87 mg121.52C(H)-0.6-0.4-0.20.0Heat Flow(W/g)406080100120140160Temperature(C)Exo UpComparison PMMA 1st Heat&2nd HeatPMMA-Aged1st Heat 10C/min6.87 mgEnthalpic Recovery PeakPMMA-Aged2nd Heat 10C/min6.87 mg-0.6-0.4-0.20.
28、0Heat Flow(W/g)406080100120140160Temperature(C)Exo UpUniversal V4.2D TA InstrumentsEnthalpy Relaxation/Recovery at TglEnthalpy relaxation,or aging,is the process of amorphous material approaching equilibrium(never reached).Energy is released as a function of time and temperaturelEnthalpy recovery is
29、 the endothermic transition seen at the end of a glass transition in DSC experiments.It is the recovery of energy that was dissipated during aginglIn traditional DSC,enthalpy recovery can appear as a melt and make measurement of Tg difficultlSince enthalpy recovery is a kinetic event,it can be separ
30、ated from the change in heat capacity by MDSCPractical Significance of Enthalpy RecoverylIs enthalpy recovery at the glass transition important?lSometimes!lIf two samples of finished product have significantly different size enthalpy recovery peaks(differ by 0.5 J/g or more),they can be expected to
31、show differences in some physical properties(size,hardness,impact resistance,etc.)lDifferences in the size of the enthalpy recovery peak for raw materials that will be processed at temperatures above Tg are not importantlThe thermal history of raw materials is usually not controlledlThese samples sh
32、ould be compared after they are heated to a temperature above Tg which removes the previous thermal historyMDSC Separation of Enthalpy Recovery PeakTotal Heat Flow includes Tg and enthalpy recovery peakReversing Heat Flow contains only TgNonreversing Heat Flow contains enthalpy recovery peakTg在哪里在哪里
33、?药片,44%RH 3.08mg MDSC 1/60/5Tg在哪里在哪里?Tg在这里在这里!Tg在这里在这里!复杂样品复杂样品Quenched Xenoy 14.79mg 10C/min复杂样品复杂样品MDSC 有助于图谱解释有助于图谱解释MDSC 有助于图谱解释有助于图谱解释无定形态无定形态 PET/PC的的DSC，PC的的Tg在哪里在哪里?MDSC 在聚合物共混物中显示两个在聚合物共混物中显示两个 Tg MDSC.318/40/3DSC 5C/min for Drug MicrospheresDSC 5C/min for Drug MicrospheresPolymer 70%Crysta
34、lline Drug 15%Amorphous Drug 15%Approx.CompositionMDSC 2C/min for Drug Microspheres聚合物合金的普通DSC淬冷 PET/PC/HDPE聚合物合金的MDSC Melting of PETMelting of HDPEZoom in on this area聚合物的MDSCTg of PETTg of PCCrystallization of PETMelting of HDPE小甜品在冷却过程中的玻璃化转变 Interpreting Change in Structure for Drug MonohydrateC
35、p of First HeatCp of Second HeatLoss of crystallinity on dehydrationRecrystallizationGlass TransitionSample analyzed in pinhole pan3、Thermoset MaterialslA“thermoset”is a cross-linked polymer formed by an irreversible exothermic chemical reactionlA common example is a 2 part epoxy adhesivelWith a DSC
36、 we can look at the curing of these materials,and the Tg of full or partially cured samplesThermosetting PolymersThermosetting polymers react(cross-link)irreversibly.A+B will give out heat(exothermic)when they cross-link(cure).After cooling and reheating,C will have only a glass transition Tg.A+B CG
37、LUEThermoset MaterialsCuring of a Thermosetting Material by DSC116.07C76.30C195.0J/g20 Min Epoxy Cured in DSC15.15mg 10C/min-6-4-202468Heat Flow(mW)050100150200Temperature(C)DSCExo UpUniversal V4.3A TA InstrumentsEffect of Heating Rate on Thermoset Curing残余固化隐藏玻璃化转变10.85 mg Epoxy heating 3/min,after
38、 isothermal cure at 100CAdvantage of MDSC for Post Cure ScanSample:EpoxySize:10.85 mgHeating Experiment at 3 C/minAfter 160 min Isothermal Cure at 100 CNote Onset of DecompositionBefore Complete CureNote Inability to Measure Tg1 1、扫描速度的影响、扫描速度的影响灵敏度随扫描速度提高而增加灵敏度随扫描速度提高而增加分辨率随扫描速度提高而降低分辨率随扫描速度提高而降低技巧
39、：技巧：增加样品量得到所要求的增加样品量得到所要求的灵敏度灵敏度低扫描速度得到所要求的低扫描速度得到所要求的分辨率分辨率DSC测试过程中的影响因素测试过程中的影响因素扫描速度的影响扫描速度的影响 大大 适用于测试低程度的转变、非均匀试样峰宽、适用于测试低程度的转变、非均匀试样峰宽、温度准确度、分辨率低。要求温度准确度、分辨率低。要求dT/dt小。小。小小 峰尖，分辨率峰尖，分辨率 好，对零级反应的转变温度好，对零级反应的转变温度 要求平衡值，允许有大的要求平衡值，允许有大的dT/dt，2、样品尺寸、样品尺寸3、气氛气氛不能与试样反应，动态优于静态。不能与试样反应，动态优于静态。高传热系数气体（
40、如高传热系数气体（如H2、He）分辨率高；分辨率高；低低传热系数气体（如真空）灵敏度高。传热系数气体（如真空）灵敏度高。样品皿的封压：底面平整、样品不外露样品皿的封压：底面平整、样品不外露样品皿的封压：底面平整、样品不外露样品皿的封压：底面平整、样品不外露合适的样品量：灵敏度与分辨率的折中合适的样品量：灵敏度与分辨率的折中合适的样品量：灵敏度与分辨率的折中合适的样品量：灵敏度与分辨率的折中样品的粒度与形状对曲线的影响样品的粒度与形状对曲线的影响4、选择合适的样品盘、选择合适的样品盘lSample Pan:Crimped vs.Hermetically SealedlCrimped pans a
41、re lighter(23mg)and provide better sensitivity and resolutionlHermetic aluminum pans are heavier(55mg)but can be sealed to prevent loss of volatileslHermetic stainless steel pans(250mg)permit use of large samples(100mg)and higher temperatures/pressures(2000 psig=1.4 MPa)lCare should be taken to keep
42、 the bottom of all pans flat to improve heat transfer/resolutionSample PanslType of pan depends on:lSample formlVolatilizationlTemperature rangelUse lightest,flattest pan possiblelAlways use reference pan of the same type as sample panHermetic Pans(Sealed)lHermetic Pans are available in:lAluminum:60
43、0C;3 atm(300 kPa gage)lAlodined Aluminum:600C;3 atm(300 kPa gage)l(For aqueous samples)lGold:725C;6 atm(600 kPa gage)lSpecialized Sealed PanslHigh Volume:100L;250C;600 psig(4.1 MPa)lHigh Pressure:35L;1000psi),in order to study decomposition by DSCOptimization of DSC ConditionslSample PreparationlKee
44、p thin;cut rather than crushlWeight of 10-15mg for polymers;3-5mg for metal or chemical meltinglGoal is to achieve a change of 0.1-10mW heat flow in going through the transition(see Figure#1)lIf sample contains volatiles,put 5-10 pinholes in the lid of the pan before crimping in order to permit a continuous evaporation process