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1、Differential Scanning Calorimetry(DSC),差示扫描量热仪(DSC),DSC测量样品吸热和放热与温度或时间的关系吸热 热流入样品，即样品吸收外界热量，为负值。放热 热流出样品，即样品对外界放出热量，为正值。,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的功率差（dH/dt）与温度(T)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 Flow,Heat flows into the sample as a r
2、esult of either Heat capacity(heating)Glass Transition(Tg)MeltingEvaporationOther endothermic processes,Endothermic,Exothermic Heat Flow,Heat flows out of the sample as a result of either Heat capacity(cooling)CrystallizationCuringOxidationOther exothermic processes,Exothermic,DSC与DTA测定原理的不同,DSC是在控制
3、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需供给的热量为纵坐标所得的扫描曲线。DTA是测量T-T 的关系，而DSC是保持T=0，测定H-T 的关系。两者最大的差别是DTA只能定性或半定量，而DSC的结果可用于定量分析。,DSC:What DSC Can Tell You,Glass Transitions（玻璃化转变，Tg）Melting and Boiling Points（熔点和沸点）Crystallization time and temperature（结晶时间和温度）Percent Crystallinity（结晶度）Polymorphism（多种形态）He
4、ats of Fusion and Reactions（熔化和反应热）Specific Heat（比热）Oxidative/Thermal Stability（氧化/热稳定性）Rate and Degree of Cure（固化速率和程度）Reaction Kinetics（反应动力学）Purity（纯度）,DSC:典型 DSC 转变,温度,热流-放热,玻璃化转变,结晶,熔化,交联(固化),氧化 或分解,热流型(Heat Flux)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温差T，然后根据热流方程，将T（温差）换算成Q（热量差）作为信号的输出。功率补偿型(Power Compens
5、ation)在样品和参比品始终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，并直接作为信号Q（热量差）输出。调制热流型(Modulated Heat Flux)在传统热流型DSC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，利用傅立叶变换将热流量即时分解成热容成分动力学成分。,1、DSC的基本原理,传统量热仪内部示意图,精确的温度控制和测量,更快的响应时间和冷却速度,高分辨率,基线稳定高灵敏度,热流DSC 炉子剖面图,热流式 DSC-工作原理,Rs,Rr,Tfs,Trs,Ts,Tr,热流式 DSC-工作原理,假设:1,传感器绝对对称，Tf
6、s=Tfr，Rs=Rr=R2,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4,样品盘及参比盘的质量（热容）相等5,样品盘、参比盘与传感器之间没有热阻或热 阻相等,Heat Flux DSC:Theoretical DT Measurement,Tr,Ts,DT,To,Tp,Tr=Reference TemperatureTs=Sample TemperatureTo=Onset of MeltTp=Peak of Melt,Theoretically:To=Tp,Time,Temperature,Actual Heat Flux Data,Slope due to th
7、ermal lag,DT,Violations of Assumptions,Pan 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
8、 rate baseline.During 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,Not Being Measur
9、ed w/Conventional DSC,Q-Series DSC Schematic,Q-Series Heat Flow Measurement,Q-Series DSC,The Tzero thermocouple provides anobjective reference point so that thosefactors previously assumed can be directlymeasured.,Tzero Heat Flow Measurement,Heat Flow Rate Equations,Heat FlowSensor Model,The sample
10、and reference calorimeter thermal resistances and heat capacities obtained from Tzero calibration are used in the heat flow rate measurements.,Differential Temperatures,Tzero Heat Flow Term Contributions,Principal heat flow provides main heat flow signalThermal resistance and heat capacity imbalance
11、 terms improve baselineHeating rate difference term improves resolution and MDSC performance,To技术的四相 热流方程,基本热流,热阻不平衡,热容不平衡,加热速率不平衡,标准DSC的单项热流方程,To技术提供的额外项,T0及高级T0技术对DSC测量的改进：,T0不需假设（Q200/Q100 DSC):1,传感器绝对对称，Tfs=Tfr，Rs=Rr=R2,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高级To不需假设(Q2000/Q1000 DSC)：4,样品盘及参比盘的质量（热容）
12、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,Baseline Bow Improvement,Superior Resolution on a Pharmaceutical Sample Analysis,Resolution Improvement,Advanced Tzero Results,MDSC 测量什么?,MDSC 将热流分解成与变化的升温速率相关和不相关的两部分MDSC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 一般来讲,只有热容与熔融的变化与变化的升温速率相关.MDSC 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
13、 原理,MDSC 同时采用两种升温速率平均升温速率提供平均升温速率，它相当与普通标准 DSC 在同样升温速率下的信号调制升温速率目的是为了在得到热流信号的同时得到热容的信号,Standard DSC Measures the Sum of Heat Flow,dH/dt=Cp(dT/dt)+(T,t),Standard DSC Measures the Sum of Heat Flow Which Arises from Multiple Sources,dH/dt=Cp(dT/dt)+(T,t),Ideal Separation of Heat Flow,dH/dt=(T,t),dH/dt=
14、Cp(dT/dt),平均&调制温度信号,调制温度,平均温度,Modulate+/-0.42 C every 40 seconds,Ramp 4.00 C/min to 290.00 C,52,54,56,58,60,62,Modulated Temperature(C),52,54,56,58,60,62,Temperature(C),13.0,13.5,14.0,14.5,15.0,Time(min),平均&调制升温速率,周期,MDSC Raw Data SignalsModulated Heat Flow and Modulated Temperature(Heating Rate),Si
15、gnals have an“Average”and an“Amplitude”,调制DSC总热流：调制热流的傅立叶转换,Calculation of Reversing Cp,Modulated Heating Rate,Modulated Heat Flow,Reversing Cp,调制DSC 不同成分的概念,MDSC 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,MDSC Data Signals,总热流=可逆热流+不
16、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部分熔融Some Melting,调制DSC 不同成分的概念,MDSC 无定形 PET,何时&为什么运行 MDSC？,我需要比热信息吗？转变是一个比热相关的现象吗?有被其他效应掩盖的现象吗？存在对于标准DSC来讲很微弱或很宽的转变吗？是否需要更高的灵敏度或分辨率吗？比热会在恒温条件下随着时间而变化吗（比如恒温
17、固化）？,何时&为什么运行 MDSC？,对于熔融和结晶 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 MDSC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,如果想得到比热(Cp)运行MDSC通过常规DSC得到比热(Q1000 由于直接比热的测量是个例外)采用较高的升温速率,10C/min需要三个实验基线参考样(蓝宝石)样品,普通 DSC的局限性,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,基线弯曲度和漂移限制了DSC
18、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,=,图谱很难解释因为DSC测量的是总热流MDSC 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.准确测量结晶度，需要:确定真正的热容基线定量测量在加热过程中有多少结晶在继续发展,ApplicationHeat Capacity Glass TransitionMelting and CrystallizationThermoplastics ThermosetsAdditio
19、nal 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 DSC 测量比热的方法:,Direct Cp Measure
20、ment on Q2000/Q1000,Unlike any other DSC,the heat flow signal of the Q2000/Q1000 is an absolute signal:Baseline is flat Absolute zero heat flow value established as part of methodBy knowing absolute values of the heat flow and the heating rate,heat capacity is calculated in real time and stored in d
21、ata fileAccuracy and precision is generally 1-2%with just single run measurements,Heat Flow and Heat Capacity from the Same Experiment,Polypropylene,It Is Often Difficult to Identify the True Baseline Using Only Heat Flow,Heat Capacity Signals Are Normalized for Heating Rate and Permit Comparison of
22、 Experiments at Different Heating Rates,Remember,DSC and MDSC Cp signals are really Apparent Cp signals;crystallization and melting are latent heats,not Cp,Effect of Side Chains on Cp,Polymer,Side Chain,Cp(J/g/C),PE,-H,2.763,PP,-CH,2.752,PS,-Ph,2.139,As the steric bulk of the side chain increases,mo
23、lecular mobility decreases resulting in lower specific heat.,B.Wunderlich,ATHAS Cp Data Bank,1985.,Effect of Polymer Backbone on Cp,#of Methylenes,Cp(J/g/C),1,0.6226,2,0.6918,3,0.7088,4,0.7597,8,0.7736,O,CH2n),O,(,As the number of methylenes increase,mobility isincreased in the polymer,resulting in
24、higher heat capacity.,B.Wunderlich,ATHAS Cp Data Bank,1985.,Polyoxyalkenes-153C,Effect of Copolymer Composition on Cp,Composition,Copolymer,Cp,(%PP),(Type),(J/C/mol),6.0,block,15.12,7.5,random,16.39,15.5,random,18.54,As PP concentration is increased,the number of methylenesincreases,resulting in a r
25、ise in specific heat capacity.Also,with randomness comes entropy（熵）,increase in mobility,and increasein specific heat capacity.,B.Wunderlich,ATHAS Cp Data Bank,1985.,PE/PP Copolymer-93C,2 Glass Transition,dQ/dt,dQ/dt,温度,温度,Tg,Tg,1/2,从DSC曲线上确定Tg的方法,PMMA 1st Heat,PMMA 2nd Heat,PMMA-Aged,2nd Heat 10C/m
26、in,6.87 mg,121.52C(H),-0.6,-0.4,-0.2,0.0,Heat Flow(W/g),40,60,80,100,120,140,160,Temperature(C),Exo Up,Comparison PMMA 1st Heat&2nd Heat,PMMA-Aged,1st Heat 10C/min,6.87 mg,Enthalpic Recovery Peak,PMMA-Aged,2nd Heat 10C/min,6.87 mg,-0.6,-0.4,-0.2,0.0,Heat Flow(W/g),40,60,80,100,120,140,160,Temperatur
27、e(C),Exo Up,Universal V4.2D TA Instruments,Enthalpy Relaxation/Recovery at Tg,Enthalpy relaxation,or aging,is the process of amorphous material approaching equilibrium(never reached).Energy is released as a function of time and temperatureEnthalpy recovery is the endothermic transition seen at the e
28、nd of a glass transition in DSC experiments.It is the recovery of energy that was dissipated during agingIn traditional DSC,enthalpy recovery can appear as a melt and make measurement of Tg difficultSince enthalpy recovery is a kinetic event,it can be separated from the change in heat capacity by MD
29、SC,Practical Significance of Enthalpy Recovery,Is enthalpy recovery at the glass transition important?Sometimes!If 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 show differences in some physical properties
30、(size,hardness,impact resistance,etc.)Differences in the size of the enthalpy recovery peak for raw materials that will be processed at temperatures above Tg are not importantThe thermal history of raw materials is usually not controlledThese samples should be compared after they are heated to a tem
31、perature above Tg which removes the previous thermal history,MDSC Separation of Enthalpy Recovery Peak,Total Heat Flow includes Tg and enthalpy recovery peak,Reversing Heat Flow contains only Tg,Nonreversing Heat Flow contains enthalpy recovery peak,Tg在哪里?,药片,44%RH 3.08mg MDSC 1/60/5,Tg在哪里?,Tg在这里!,T
32、g在这里!,复杂样品,Quenched Xenoy 14.79mg 10C/min,复杂样品,MDSC 有助于图谱解释,MDSC 有助于图谱解释,无定形态 PET/PC的DSC，PC的Tg在哪里?,MDSC 在聚合物共混物中显示两个 Tg,MDSC.318/40/3,DSC 5C/min for Drug Microspheres,Polymer 70%Crystalline Drug 15%Amorphous Drug 15%,Approx.Composition,MDSC 2C/min for Drug Microspheres,聚合物合金的普通DSC,淬冷 PET/PC/HDPE,聚合物
33、合金的MDSC,Melting of PET,Melting of HDPE,Zoom in on this area,聚合物的MDSC,Tg of PET,Tg of PC,Crystallization of PET,Melting of HDPE,小甜品在冷却过程中的玻璃化转变,Interpreting Change in Structure for Drug Monohydrate,Cp of First HeatCp of Second Heat,Loss of crystallinity on dehydration,Recrystallization,Glass Transiti
34、on,Sample analyzed in pinhole pan,3、Thermoset Materials,A“thermoset”is a cross-linked polymer formed by an irreversible exothermic chemical reactionA common example is a 2 part epoxy adhesiveWith a DSC we can look at the curing of these materials,and the Tg of full or partially cured samples,Thermos
35、etting Polymers,Thermosetting 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.,Thermoset Materials,Curing of a Thermosetting Material by DSC,Effect of Heating Rate on Thermoset Curi
36、ng,残余固化隐藏玻璃化转变,10.85 mg Epoxy heating 3/min,after isothermal cure at 100C,Advantage of MDSC for Post Cure Scan,1、扫描速度的影响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技巧：增加样品量得到所要求的灵敏度低扫描速度得到所要求的分辨率,DSC测试过程中的影响因素,扫描速度的影响,大 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dT/dt小。小 峰尖，分辨率 好，对零级反应的转变温度 要求平衡值，允许有大的dT/dt，,2、样品尺寸,3、气氛不能与试样反应
37、，动态优于静态。高传热系数气体（如H2、He）分辨率高；低传热系数气体（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,AgNO3的DSC曲线 a.原块状样品 b.稍研磨样品 c.先熔化冷却后再测,拉伸过PET的 DSC曲线,未拉伸PET的 DSC曲线,4、选择合适的样品盘,Sample Pan:Crimped vs.Hermetically SealedCrimped pans are lighter(23mg)and provide better sensitivity and resolutionHermetic a
38、luminum pans are heavier(55mg)but can be sealed to prevent loss of volatilesHermetic stainless steel pans(250mg)permit use of large samples(100mg)and higher temperatures/pressures(2000 psig=1.4 MPa)Care should be taken to keep the bottom of all pans flat to improve heat transfer/resolution,Sample Pa
39、ns,Type of pan depends on:Sample formVolatilizationTemperature rangeUse lightest,flattest pan possibleAlways use reference pan of the same type as sample pan,Hermetic Pans(Sealed),Hermetic Pans are available in:Aluminum:600C;3 atm(300 kPa gage)Alodined Aluminum:600C;3 atm(300 kPa gage)(For aqueous s
40、amples)Gold:725C;6 atm(600 kPa gage)Specialized Sealed PansHigh Volume:100L;250C;600 psig(4.1 MPa)High Pressure:35L;300C;1450 psig(10 MPa)Note:3 atm is approximately 44 psig,Factors Affecting Sensitivity/Resolution,Thermocouple OutputMagnitude of DTSignal/NoiseBaseline QualityTime Constant of Transd
41、ucerPan Contact Resistance,Sensitivity,Resolution,The flatness of the bottom of the DSC pan in critical to optimizing resolution,It Does Matter What Pan You Use,Monohydrate Pharmaceutical sample,How do we keep DSC cells clean?,DO NOT DECOMPOSE SAMPLES IN THE DSC CELL!Run TGA to determine the decompo
42、sition temperature Stay below that temperature!Make sure bottom of pans stay cleanUse lidsUse hermetic pans if necessary,Optimization of DSC Conditions,Experimental Conditions(cont.)Select an end-temperature which does not cause decomposition of the sample to occur in the DSC.Decomposition products
43、can condense in the cell and cause either corrosion of the cell or baseline problems Use sealed glass ampoules or stainless steel pans,which can take high pressure(1000psi),in order to study decomposition by DSC,Optimization of DSC Conditions,Sample PreparationKeep thin;cut rather than crushWeight of 10-15mg for polymers;3-5mg for metal or chemical meltingGoal is to achieve a change of 0.1-10mW heat flow in going through the transition(see Figure#1)If sample contains volatiles,put 5-10 pinholes in the lid of the pan before crimping in order to permit a continuous evaporation process,
