Materials You Know - Chemistry Coursescourses.chem.psu.edu/chem112/Fall/Lecture Notes/LSV Lecture...

1 CHEM 112 LRSVDS Materials

Modern Materials and PSU Research •! First school to offer a materials curriculum in 1960. Developed the first

interdisciplinary materials laboratory in 1962.

•! Penn State is ranked #1 in the US in expenditures for materials research, $50,000,000

•! Penn State’s Materials Research Institute (MRI) is one of the Materials Science and Engineering Centers funded by NSF (MRSEC, www.mrsec.org); interdisciplinary research groups working on:

–! Biomolecular / Biomimetic Materials

–! Condensed Matter Phenomena

–! Energy / Sustainability

–! Mechanics of Materials

–! Multiferroics / Magnetics / Spintronics

–! Nanostructures / Nanoparticles

–! Polymers

–! Semiconductors / Photonics / Organic Electronics

–! Soft Materials / Colloids

•! 200+ faculty members, 100 Researchers, and 800 Graduate Students are associated with MRI. 15 Academic departments, 5 colleges

•! 21 research centers housed at Penn State are currently working on materials research including:

•! Center for Nanoscale Science

•! Particulate Materials Center

•! Carbon Research Center

•! Center for Dielectric Studies


Materials You Know

Material: Zeolites for water

softening.

Different amounts of zeolites

in detergents depending on geographic location.

Sodium Zeolite A

Material: Kevlar for bullet

proof vests.

Polymer structure produces strong

intermolecular forces for a

strong material. Kevlar

Ceramics (inorganic, nonmetallic solids)

Polymers


Polymers

The chemistry of compounds containing C bonded to H.

!Also may contain O, N, S, and halogens

Reasons for large numbers of organic compounds:

1.! Carbon atoms can form strong, stable bonds to other C atoms (small size)

2.! Carbon atoms form up to 4 bonds simultaneously: (valence of 4)

3.! Carbon atoms can form multiple bonds (Small size and valence of 4)

4.! The C-H bond is nonpolar, but bonds to other elements are polar (N, O, halogens). (electronegativity)

Review Organic Chemistry


Classes of Organic Compounds Classification is necessary to manage the large number of

compounds

Classes of HYDROCARBONS: Contain only C and H (Simplest organic compounds)

1) alkanes all single bonds

2) alkenes one or more double bonds

3) alkynes one or more triple bonds

4) aromatic alternating single and double bonds in a ring

C C

C C

H

H

H

H

H

H

benzene


Addition Reactions C-C Double and triple bonds are reactive: addition

reactions typically occur at room temperature.

For Alkenes

CH3#CH=CH2 + Br2 $

CH3#CH=CH#CH3 + HX $ where X = Cl, Br, I, OH, etc.

For Alkynes CH3 #C%CH + 2 Br2 $

CH3-C % C -CH3 + 2HCl $

C C C C H

H

H

H

H

H

H H

X H

C C C H

H

H

H

H H

Br Br

C C C H

H

H

H

Br Br

Br Br

C C C H

H

H

H

H H

Cl Cl


Functional Group Classes •! Contain a representative group of elements in a fixed pattern:

•! Each class has similarities in structure and function (reactivity)

•! R, R’, R” = alkyl group

Alcohols R-OH R"H

Ethers R-O-R’ R and R’"H

Amines

Functional Groups which contain a carbonyl group

Aldehydes Ketone (R and R’"H)

Carboxylic Acid Ester Amide

N H

R

H N R'

R

H N R'

R"

R

C

O

C

O

R HC

O

R R'

C

O

R OHC

O

R OR'C

O

R NHR'


Condensation Reactions Two molecules join by eliminating a small molecule (such as

water)

Ethers, Esters, and Amides are formed via condensation reactions:

alcohol + alcohol #$ ether + water

R#O#H + H#O#R’ #$ R#O#R’ + H2O

carboxylic + alcohol $ ester + water

acid

+ H#O#R’ $ + H2O

carboxylic + amine $ amide + water

acid

+ $ + H2O

C

O

R OH

C

O

R OR'

C

O

R NHR'

N H

R

H

C

O

R OH


High molecular weight materials formed from many small

molecules called monomers

Monomer = repeating unit

What Materials do you know are Polymers?

Polymer Synthesis 1.! Addition polymers

Monomer contains a double bond; polymers form via addition reactions

Examples: Rubber, Cross-linking of PVA

2.! Ring opening Cyclic monomer opens to form a linear chain

(such as the polymerization of Sulfur)

3.! Condensation polymers

polymers form via condensation reactions

a small molecule (H2O, HCl, CO2) is eliminated in the reaction

Example: Silicone polymers

POLYMERS


Double bond opens up, two electrons are used to form two new C-C single bonds connecting monomers

Styrofoam (Polystyrene) Addition Polymer

C C

H

H

H

H2C

HC

n


H H

CC

H H

CH2CH2

F F

CC

F F

CF2CF2

H

CC

H H

CH2CH

n

n

n

H Cl

CC

H H

CH2CH

n

Cl

ethylene

H C

CC

H CH3

CH2C

n

C

O

O

CH3

O O

CH3

CH3

polyethylene(gladwrap)

tetrafluoroethylene Teflon,TFal

stryrene polystyrene(Styrofoam)

vinyl chloride polyvinyl chloride(PVC)

methyl methacrylate MMA polyMMA (Plexiglass)


Rubber: A naturally occurring Addition

Polymer


Condensation Polymerization Two molecules join to form a larger molecule by elimination of a

small molecule such as water

Cyclic monomer opens to form a linear chain

Ring Opening Polymerization

R'

OOHN

R

O

HN

On

Polyurethane Used in: foam furniture stuffing spray-on insulation auto parts water-protective coatings


Condensation Polymers

Nylon 6,6 (polyamide)

(CH2)4

C

OH

O

C

HO

O

N (CH2)6

H

H

N

H

H

(CH2)4

C

O

C

O

N (CH2)6 N

H

H

+


Properties of polymers Polymers form glasses

Above Tm: polymer is liquid-like (fluid chains)

Below Tm: wants to crystallize, but can’t

Between Tm and Tg= elastomer

Tg = glass transition temperature: substance becomes amorphous solid (glass)

Elastomer turns to a brittle solid…


Properties depend on:

1)! Degree of Crystallinity; how does it pack together?

!!

!!

!!

2)! Interactions between chains; cross-linking

!!

!!

Properties of Polymers


Degree of crystallinity: amount of ordering in a polymer

Polymer chains tend to be flexible and easily entangled or folded; tend to be disordered

! hard to crystallize; often amorphous

Crystallinity affects optical properties:

1) Amorphous polymers are transparent (glasslike) 2)! Polymers that are partly crystalline and partly glassy

are translucent

Crystallinity affects physical properties: crystalline polymers are stiffer, harder, more dense


Increasing order in a polymer

Interactions between chains of a polymer lend elements of order to the structure of polymers.

Stretching (or extruding) the polymer chains as they form can increase the amount of order, leading to a greater degree of crystallinity in the polymer.


Factors that affect Crystallinity

Atactic is amorphous: Doesn’t pack well: used to make flexible plastics (garbage bags)

Isotactic packs well; is more crystalline. Plastics will be stiffer: used to make tupperware

1) Side chains can affect packing and crystallinity:

2) Average molecular mass affects degree of crystallinity: compare

low and high density polyethylene

HDPE: average

molecular mass of

106 amu

LDPE: average

molecular mass of

104 amu


Interactions between chains

•! Crosslinking: covalent bonds between chains: increases stiffness, strength. Examples: rubber, PVA, Silicone

•! Metal ions can serve as cross-linking agents Example: Sodium alginate

•! Intermolecular forces can hold polymer chains together:

a) LDF’s hold chains in nonpolar polymers together:

Polyethylene, polypropylene

b) dipole-dipole

c) Hydrogen-bonding plays an important role in biological polymers

DNA, Proteins


Vulcanization of Rubber Bonds formed between chains make the polymer stiffer; more

crystalline

•! Natural rubber is too soft and chemically reactive to make a useful material.

•! By vulcanizing the rubber (crosslinking the chains with sulfur) useful materials are made.

Isoprene

(monomer)

Natural rubber

(gummy)

Cross-linked rubber

(tough elastomer)

S8

heat H2C CH2

H3C


Crosslinking

C=C H

H

H

OH vinyl alcohol

catalyst

heat

poly(vinyl alcohol)

linear chain polymer, x = 103 - 104

viscoelastic

CH2

CH

CH2

CH

HO OH

x

Add a cross-linker: borax, B4O72- (forms covalent crosslink)

Poly(vinylalcohol): An Addition Polymer

CH2

CH

CH2

CH

CH2

O

O

CH

CH

O

O

CH2

CH

CH2

CH

CH2

O

O

CH

CH

O

O

B

B

B

CH2

CH

CH2

CH

CH2

O

O

H

H

CH

CH

O

H

O

H

CH2

CH

CH2

CH

CH2

O

O

H

H

CH

CH

O

H

O

H

+ B4O72- "


Crosslinking with Metal Ions 2 Sodium alginate + CaCl2 $

http://www.lsbu.ac.uk/water/hyalg.html

Top view


Silicones condensation polymers

#!chains of alternating silicon and oxygen atoms with organic substituents on the silicon.

Monomer: silicon compound with organic groups (R) attached. R2SiCl2

Example:

dichlorodimethylsilane [(CH3)2SiCl2] with water (H2O).

The silicone formed is dimethylsiloxane.

Silicones are either rubbers or oils depending on the chain length and degree of cross-linking.

Lubricants Car polish

Gaskets, sealants Waterproofing (organic groups form barrier)


Cross-Linking Affects Properties of Silicones

Properties of Silicones Nontoxic, stable, unreactive

Flame-resistant

hydrocarbon substituents act to repel water.

Properties depend on: 1)! R-group

2)! Chain length

3)! Degree of cross-linking

–! No crosslinks; liquid silicone oils

high T lubricants, hot oil baths

–! Few cross links; silicone rubber

caulking material

–! More cross links; silicone resins

coatings and adhesives

–! All cross links; SiO2 = quartz


1)!

2)!

3)!

4)!

5)!

Summary: What holds polymers together?


Uses of Polymers in Smart Sensors

•! Polymers play an important role in modern sensors

•! Polyvinylidene Fluoride (PVDF) is one of the main polymers used to make smart sensors.

Monomer: Polymer:

C C

H

H

F

F

C C

H

H

F

F

**

When a film of PVDF is stretched, the F atoms align on top and the H atoms on the bottom, producing a vertical dipole moment.

The dipole moment in PDVF gives it piezoelectric properties. The

piezoelectric effect is the ability of a material to produce a voltage when subject to mechanical stress.

The stretched PVDF film can be attached to electrodes.

Bending the film will produce a voltage by fanning out the dipole moments.

n

27

C C

H

F

F

F

**

C C

H

H

F

H

**

CHEM 112 LRSVDS Materials

Other Piezoelectric Polymers PVDF is not the only polymer that is piezoelectric.

•! Polyvinyl Fluoride (PVF):

Monomer: Polymer:

C C

H

H

F

H

Polytrifluoroethylene (PTRIF) Monomer: Polymer:

n

n

C C

H

F

F

F

The monomer must be polar.

The atoms bonded to the polymer backbone must be small.

Fluorine is common in piezoelectric polymers because of its size and electronegativity.

Properties of Piezoelectric Polymers


Biological Polymers 1. DNA, RNA

Monomers: nucleotides

React via condensation polymerization

DNA and RNA are polyesters (of H3PO4).

2. Proteins

Monomers: amino acids

React via condensation polymerization

Proteins are polyamides.

N C C

H

H

H

R

O

OH

N C C

H

H

H

R

O

OH

N C C

H

H

H

R

O

OH

+ +

N C C

H

*

H

R

O

N C C

H

R OH

N C C

H

R

O

*

H

Product: Protein

amide linkage or peptide bond

Amino Acid Monomers:


Structure of Proteins

Tertiary structure (protein

folding) is even more

complex. This structure is

important in protein activity.

Secondary structure

of proteins:


DNA (Deoxyribonucleic Acid)

Monomer; nucleotide

Polymer; polynucleotide RNA (Ribonucleic Acid):


Hydrogen Bonding in DNA


DNA

replication

What kind of forces? Crosslinking in DNA:


Biomaterials are any materials that have biomedical applications.

For example, the materials that are used to fill teeth are biomaterials.

Physical requirements:

Different for each specific environment.

For example, artificial heart valves

must open and close 70 to 80

times per minute.

Biocompatiblity:

The body’s immune system must not attack the biomaterial.

Characteristics of Biomaterials

Chemical requirements:

Biomaterials must be of medical grade.

Must be biodegradable or non-reactive: beware of fillers, stabilizers, etc.


The degree to which the body tolerates foreign materials

depends on the nature of the atomic groups in the material.

Naturally occurring biomaterials are polymers of sugars (polysaccharides), nucleotides (RNA, DNA) and amino acids (proteins, enzymes, etc.).

Types of Polymers

Plastic: materials that can be formed into shapes.

Thermoplastic: materials that can be shaped more than once. (Used as

replacements for blood vessels.)

Thermosetting: materials that can only be shaped once (Used in dental devices,

and orthopedics such as hip replacements.)

Elastomer: material that is elastic in some way. If a moderate amount of

deforming force is added, the elastomer will return to its original shape.

Used as catheters, and for covering leads on implanted electronics, like

pacemaker.

Polymeric Biomaterials


Heart Replacement and Repairs:

Polyethylene terephthalate, called

Dacron™, is often used in the manufacture

of artificial heart valves.

Dacron™ is used because tissue will grow

through a polyester mesh.

Vascular grafts:

C C

F

F

F

F

**

Examples of Biomaterial Applications

A vascular graft is the replacement for a

piece of blood vessel.

Dacron™ is used for large arteries.

Polytetrafluoroethylene, is used for smaller

vascular grafts.


Artificial Tissue: •! Artificial skin, which is grown in the

laboratory, is used to treat patients with extensive skin loss.

•! The challenge with growing artificial skin is getting the cells to align properly.

•! Therefore a scaffold must be used for the cells.

•! The most successful scaffold is lactic acid-glycolic acid copolymer.

Examples of Biomaterial Applications

Hip Replacements: •!About 200,000 total hip replacements are performed each year. •!A metal ball, a cobalt chromium alloy, is often used in a hip replacement. •!This alloy is attached to a titanium alloy and cemented using a tough thermoset polymer. •!The acetabulum, which accommodates the femur, is lined with a polyethylene layer

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Chem 112!

Congratulations!

Now, go ace that final!

Materials You Know - Chemistry Coursescourses.chem.psu.edu/chem112/Fall/Lecture Notes/LSV Lecture...

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