Lec 3 Flashcards

(14 cards)

1
Q

Glass-Transition Temperature (Tg)

A

Tg is a measure of the energy required to break the bonds and fluidize the material

Above Tg -> fluid

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2
Q

viscosity vs MW

A

log viscosity proportional to log MW

Lower viscosity and lower MW makes mvm easier

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3
Q

Elastic vs viscous materials G

A

Elastic solids store energy → characterized by G’ (storage modulus).

Viscous fluids dissipate energy → characterized by G’’ (loss modulus).

G’ > G’’ → solid-like
G’’ > G’ → fluid-like

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4
Q

Alpha actinin vs filamin

A

Alpha-actinin (ACTN)
Forms parallel actin networks

Filamin (FLN)
Forms orthogonal actin networks

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5
Q

Affine material mech response

A

Non-affine (not aligned) networks have non-linear responses to shear

very low (or high) cross linker to filament ratio leads to Anisotropic filament bundling

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6
Q

How does crosslink density influence mechanics?

A

Crosslinking increases elastic modulus (G’), but does not affect dissipation timescale

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7
Q

What does G’ > G’’ indicate?

A

Solid-like behavior

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8
Q

What determines mesh size in actin networks?

A

Inversely proportional to square root of actin concentration

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9
Q

How does stress stiffening arise in a network

A

Stress stiffening arises not from bond deformation, but from entropy loss in semiflexible polymers (lose slack)

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10
Q

What does peak in G″ (loss) mean

A

timescale where maximum energy dissipation occurs

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11
Q

What does increasing applied stress do to a network

A

Stiffens

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12
Q

What happens to the loss tangent (G″/G′) when myosin is added?

A

It decreases, indicating the network becomes more solid-like

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13
Q

What does a decreasing loss tangent (G″/G′) indicate about the material?

A

That it is becoming more solid-like, storing more energy than it dissipates

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14
Q

How is the stiffening effect modulated by actin concentration?

A

Higher actin concentration → more filament overlap → stronger stiffening by motors

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