molecular and supramolecular understanding of

MAT 2020MÉTODOS DE ANÁLISE TÉRMICA

DQB... 2019-2020

DSC … Metodologia e Aplicações

2II Jornadas Nacionais de Caracterização de Materiais

Energy balances.

Chemical reactions

Physical processes

Materials Characterization

Biophysics/Biochemistry

Engineering

to measure and follow heat changes in processesCalorimetry:


But Heat , q... Is not possible to measure directly

e.g. Heat flux ...versus... Time



e.g. Heat flux ...versus... Time

T heatT

time

time


Seems to be a old-fashioned subject !!

Low-tech apparatus / methodology!!




DEPENDS:

Size of the Sample / Process

How strong is the heat change

What heat change we want to measure

Which process we want to follow

RESOLUTION/ACCURACY measurement

• isoperibolic (static and dynamic)

• heat exchanging (isothermal and temperature scanning)

• adiabatic (static and dynamic)

To measure lots of HEAT.... (e.g Chemical Reaction..combustion)

Temperature homogeneity

Lots of heat involved

MOTOR

Local

T control

Heating

cooling

Precise

T control

T measurement>Isoperibol Calorimeter

8

Adiabatic TEMPERATURE CHANGECombustion calorimeter

Local

T control

Region

T change

High heat capacityReasonable time constant

Fixe

d T

emp

erat

ure

dT/dt = u + k(TJ - T)

T(t) = T - (T - Ti)exp{- k(t – ti)}

T(t) = Ai + Bi t + Ci t2 + Di t3

ISOPERIBOLLong time to reach the temperatureStationary and uniform temperature

T

Tf

(tx)Te

mp

erat

ure

, T

t

c

t

b

tx

main period

T i

(tx)

(a)

A

BTf

(tc)

T i

(tb)

Example ..Combustion bomb

9

Local

T control

Region

T change


Fixe

d T

emp

erat

ure

T

T (tx)f

T' (t’x)f

Tem

per

atu

re,

T

tcTime, ttb tx t’x

Polynomial

Exponential

main period

(b)

T (tc)

dT/dt = u + k(TJ - T)

T(t) = T - (T - Ti)exp{- k(t – ti)}

T(t) = Ai + Bi t + Ci t2 + Di t3

ISOPERIBOLLong time to reach the temperatureStationary and uniform temperature

Combustion calorimeter

10

Local

T control

Region

T change


Fixe

d T

emp

erat

ure

Heat/energy content of :

Materials

Food

Fuels

Chemicals

Typical Comercial Combustion calorimeter

11

DSCSmal samples and low HEAT change involved

Differential Calorimetry / Microcalorimetry

temperature flutuation of the furnace

Strategy to cancel :

heat capacity of the cell/container

12

Calvet-typeHeat flux

Different type of Differential calorimeters

Differential power

Reaction

13

MicroCal VP-DSC

Setaram mDSC III

DSCHeat flux

Differential power

Differential Scanning Calorimetry / Microcalorimetry

temperature flutuation of the furnace

Strategy to cancel :

heat capacity of the cell/container

Sample temperature correction

Scanning > Temperature scan rate


Amostra e referência

instalados no mesmo

forno

Termopares

Amostra Referência

Amostras e referência em

Fornos independentes

Sensor de fluxo e aquecedor

Amostra Referência


Heat Flow DSC Power compensationDSC


Differential Scanning Calorimetry / Microcalorimetry


Ionic liquid

Thermal & Phase Behavior ….

CnC1im [PF6]

Differential Scanning Calorimetry

Thermal Behavior

CAL ...n=6

Differential Scanning Calorimetry

Thermal Behavior

Ionic liquid

19



Flash Differential Scanning Calorimetry (Flash DSC)

20


Scanning > Temperature scan rate (cooling)


21


Scanning > Temperature scan rate (cooling)


Low-tech ???

Quite high-tech!!

22

Calvet Microcalorimetry drop methodDirect determination of vaporization enthalpies

Capilary tubes: 20 – 30 mgSample: 3 – 5 mg ∆g

cr/lHo

m (T=298.15 K) = ∆g, Tcr/l, 298.15 KHo

m —∆T298.15 KHo

m(g)

“Drop methodology”

Tf K

TiK

<T> = 298.15 K

23

Calvet type Microcalorimetry

24

Time/ s

0 500 1000 1500 2000 2500 3000

Hea

t fl

ow

/ m

W

-12

-10

-8

-6

-4

-2

0

2

Flu

xo

tér

mic

o /

mW

Tempo / s

Sample Reference

Initial Temperature

Calorimeter

Temperature

Vacuum

~ 100 seconds

Calvet Microcalorimetry drop method

)(0g

l THm

T

.p dT)l(C

15298

0

m

g,

298.15 l, HT

T

p dTgC15.298

)(

K)(298.150

m

g

lH

IL (l, T = 298.15 K) IL (g, T =298.15 K)

IL (l, T ) IL (g, T )

)(0g

l THm

T

.p dT)l(C

15298

0

m

g,

298.15 l, HT

T

p dTgC15.298

)(

K)(298.150

m

g

lH

IL (l, T = 298.15 K) IL (g, T =298.15 K)

IL (l, T ) IL (g, T )

Calvet Microcalorimetry drop method

26

Calvet Microcalorimetry drop methodDirect determination of vaporization enthalpies


TiK

<T> = 298.15 KJACS… Ionic liquids: First direct determination of their cohesive energy

Tf K

27

DSC & mDSC

Step or Continuos Scan Mode

e.g. Heat capacity measurements

28

DSC & mDSC

Step or Continuos Scan Mode

e.g. Heat capacity measurements

29

Drop Differential Microcalorimetry


293.15 K

303.15 K

<T> = 298.15 K

Calorimeter (Tf)293.15 K

Furnace (Ti)303.15 K

Very accurate Heat capacity measurements

Bloco Calorimétrico (Tf)

Oven (Ti)exo

Drop Differential Microcalorimetry

Is proportinal to theArea

Cp

Very accurate Heat capacity measurements

High-Precision Heat Capacity Drop Calorimeter

N

2 4 6 8 10 12 14 16 18 20

Co

p /V

/

J·K

-1·c

m-3

1.86

1.88

1.90

1.92

1.94

1.96

1.98

2.00

2.02

Heat Capacities of Ionic Liquids – Cp /V= f(N), T=298.15 K

Heat Capacity ..Data

CAL ...n=6

Alkyl Side Chain Length effect

CAL ...N=2x6 =12

So

lva

tio

n

AlcoholsIonic Liquids

DifferentialHeat Flux Signal

R S

ITC Isothermal Titration Calorimetry ,

Solvation of alcohols in Ionic Liquids

MOLECULAR PROBES

What solvation says about the Nanostructuration in ILs?

Solvation of alcohols in Ionic Liquids (ITC)

[CN-1C1im][NTf2]

Alkyl side chain length (N = 3 – 13)

AlcoholsTrend Shift .. C6C1imNTf2

MOLECULAR PROBES

34

K, H, S

ITC, Microcalorimetry

35

Microcalorimetry

36

DSC & mDSC

Phase diagrams C2C1 C3 C4

37

DSC & mDSC

Phase diagrams

Mixtures of Hexadecane - Methyl Stearate ..mole fraction ....0.1

38

DSC …phase diagrams


Is quite powerful and unique !

Calorimetry: is used to measure the heat flux associated with physical and chemical transformations.

ANDto measure/follow/identify, phase change, equilibrium, chemical and physical kinetics, etc.

molecular and supramolecular understanding of

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