麻省理工-高分子物理1

3.063 Polymer PhysicsSpring 2007 Viewpoint:somewhat more general than just polymers:

“Soft Matter”Polymers, Colloids, Liquid Crystals, Nanoparticles and Hybrid OrganicInorganic Materials Systems.Reference: Young and Lovell, Introduction to Polymer Science (recommended) Demos and Lab Experiences: Molecular Structural Characterization (DSC, GPC, TGA, Xray, AFM, TEM, SEM…) and Mechanical& Optical Characterization

Course Infoeltweb.mit.edu/3.063 - course website: notes, hmwks… Eric Verploegen Ms. Juliette Braun Office hours - How are Wednesdays at 230-330pm? Mini Assignment Send Prof. Thomas

– contact info/ name/year/major/email/credit/listener– and interests relevant to topics in this course– Any expertise you have on lab demos, characterization tools, cool samples…

Hard vs. Soft Solids(for T~ 300K) Hard matter: metals, ceramics and semiconductors: typically highly crystalline. U>> kT Soft matter: polymers, organics, liquid crystals, gels, foods, life(!). U~ kT Soft matter is therefore sometimes called“delicate material” in that the forces holding the solid together and causing the particular atomic, molecular and mesoscopic arrangements are relatively weak and these forces are easily overcome by thermal or mechanical or other outside influences. Thus, the interplay of several approximately equal types of forces affords the ability to access many approximately equal energy, metastable states. One can also“tune” a structure by application of a relatively weak stimulus. Such strong sensitivity means that soft matter is inherently good for sensing applications.

In 3.063 we aim to understand: The Key Origins of Soft Solid Behavior:relatively weak forces between molecules many types of bonding, strong anisotropy of bonding (intra/inter) wide range of molecular shapes and sizes, distributions large variety of chemistries/functionalities fluctuating molecular conformations/positions presence of solvent, diluent entanglements many types of entropy architectures/structural hierarchies over several length scales

Characterization of the molecular structures and the properties of the soft solids comprised of these molecules

Scale in Soft Matter1

DuPont microstructured fibers.

DNA molecule AFM

0.8

Human Hair Carbon nanotube Photoresist (150 nm) 2-photon polymerizedphotonic crystal Nature 1999

0.6

0.4

0.2

Red blood cells Intel 4004 Virus10 4 10 3 10 2 10 1

0 106

10 5

Patterned atoms10 0

Dimensions (nm)

Interactions in Soft Solids Molecules are predominantly held together by strong covalent bonds. Intramolecular - Rotational isomeric states Intermolecular potential– Hard sphere potential– Coulombic interaction– Lennard Jones potential (induced dipoles)– Hydrogen bonding (net dipoles) “hydrophobic effect” (organics in water)

Polyelectrolyte Domain Spacing Change by e-FieldQP2VP

PS

Apply field

Photo of tunable gels removed due to copyrig

ht restrictions.

Fluid reservoir

Initial film thickness:~ 3μm Total# of layers:~ 30 layers

nPS - nP2VP~ 1.6 nH2O= 1.33

Structure of Soft Solids SRO - (always present in condensed phases)– intra- and inter-

LRO - (sometimes present)

– Spatial: 1D, 2D, 3D periodicities– Orientational

Order parameters (translational, orientational…) Defects -

– influence on properties; at present defects are largely under-appreciated;– e.g. transport across membranes…self assembly-nucleation, mutations, diseases

Manipulation of Orientation and Defects: Develop methods to process polymers/soft solids to create controlled structures/hierarchies and to eliminate undesirable defects

Polymers/MacromoleculesH. Staudinger (1920’s)colloidal ass’y vs. molecule

“MACROMOLECULAR HYPOTHESIS”

single repeating unit (MER)

covalent bonds

A SINGLE REPEAT UNIT MANY REPEAT UNITS

→ MONOMER (M)→ POLYMER (M)n

“Macromolecule” - more general term than polymer

POLYMERIZATIONCommon reactions to build polymers: 1. Addition: Mn+ M→ Mn+1 2. Condensation: Mx+ My→ Mx+y+ H2O or HCl/ etc.How do the properties change with n?

Think of a polymer as the endpoint of a HOMOLOGOUS SERIES: nDegree of Polymerization

N=

1

2

3

Example: Polyethylene (n≈ 104)CH2=CH2→–

monomer

CH2– CH2– n<100– CH2– CH2–→

oligomer

polymer

n≥100

Proteins and Polyamides (Nylons)Proteins are“decorated nylon 2”H N H

O

R

n

R= various side groups (20 possible amino acids) R= H→ glycine R= CH3→ alanine, etc.

H N O

H N O

H N O

amide linkage Members of the nylon family are named by counting the number of carbon atoms in the backbone between H H nitrogen atoms.H nylon 2O H N CH2 O H CH2 N5

H N O H N

H N O H N O O

H N O H N

N

CH2 O

N

Tm> 300°C

H CH2 N5

nylon 6O

N

Tm= 215°C

O

O6 carbon atoms

O

Hydrogen bondsTm~ 140°C

note nylon n=∞= polyethylene (!)

Characteristic Features of Macromolecules Huge Range of Structures& Physical Properties Some examples: Insulating --------> Conducting Light emitting Photovoltaic, Piezoelectric Soft elastic ---------> Very stiff plastic Zero/few crystals ------> High Crystallinity

– Ultra large reversible deformation– Highly T, t dependent mechanical properties

Readily Tunable Properties:Weak interactions between molecules, so chains can be readily reorganized by an outside stimulus

Chain Conformations of Polymers: 2 Extremesn is the number of links in the chain with each link a step size l so the contour length of the chain L is nl; As a measure of size of the chain, we can have two situations:…… 此处隐藏：4111字，全部文档内容请下载后查看。喜欢就下载吧 ……