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Morphology assessment of polymer hydrogels using multivariate analysis of viscoelastic and swelling properties Evgeny Karpushkin, Andrey Bogomolov WSC-9,

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Presentation on theme: "Morphology assessment of polymer hydrogels using multivariate analysis of viscoelastic and swelling properties Evgeny Karpushkin, Andrey Bogomolov WSC-9,"— Presentation transcript:

1 Morphology assessment of polymer hydrogels using multivariate analysis of viscoelastic and swelling properties Evgeny Karpushkin, Andrey Bogomolov WSC-9, Tomsk, Feb 2014

2 What is hydrogel? Large variety of gels, but in this talk gel = covalently cross-linked 3D (network) polymer swollen in water Properties: hydrophilic, swollen, soft materials biocompatible or biodegradable responsive to changes of temperature, pH and ionic strength; electrical and magnetic fields Applications: artificial implants (contact lens) supports for enzymes and cells immobilization sensors, actuators, chemical valves and robots models of tissues and organs food industry, cosmetics, …

3 Examples of hydrogel morphology: polyHEMA Soft Matter 3 (2007) 1176–1184 Reactive & Functional Polymers 62 (2005) 1–9 Macromolecules 40 (2007) Biomaterials 26 (2005) 1507–1514 Pores generation in HEMA gels: phase separation during polymerization incorporation of soluble particles cryo (frozen solvent as porogen) liquid porogen (emulsion polymerization) introduction of gas generating substances Journal of Controlled Release 102 (2005) 3–  m 400  m 1 mm

4 Materials science: general aim Preparation conditions Structure: porosity, topology, microphases, … Structure: porosity, topology, microphases, … Utilitarian properties How do preparation conditions influence the material structure? How does structure of material influence its functional properties? What material structure corresponds to certain measured properties? How to prepare a material with desired properties? Measured properties Composition

5 Remarks on microscopy Light microscope: rapid, good for start, but resolution not enough Electron microscope: for dry samples structure is not always preserved Electron microscope: for swollen samples observed structure is highly dependent on conditions Chamber pressure decreasing dry swollen

6 Preparation of samples diluent (NH 4 ) 2 S 2 O 8 glass plates rubber sealing diluent content diluent nature (water, aqueous NaCl, aqueous Mg(ClO 4 ) 2 ) cross-linker : monomer ratio swelling medium: water, dimethylsulfoxide, aqueous NaCl HEMA DEGDMA TEMED APS (0.1M NaCl) 70/1 (DMSO) diluent typediluent ratio (wt%) crosslinker to monomer ratio (mol%) swelling medium Sample code Variable parameters: > 100 samples

7 Observed properties Morphology type Equilibrium swelling Shear deformation Homogeneous Droplets Interlocking Fused particles Mixed In water, or DMSO, or aqueous NaCl Sometimes versus temperature Forced oscillatory deformation Creep (constant shear stress in time)

8 Morphology of hydrogels: diluent at preparation = water

9 Morphology of hydrogels: salting-in diluent at preparation 70/2 (0.05M Mg(ClO 4 ) 2 )70/2 (0.2M Mg(ClO 4 ) 2 )70/2 (0.3M Mg(ClO 4 ) 2 )70/2 More diluent solvating power = less phase separation

10 Morphology of hydrogels: salting-out diluent at preparation 60/1 (0.2M NaCl)60/1 (0.4M NaCl)60/1(0.45M NaCl)60/1 (0.475M NaCl)60/1 (0.5M NaCl)60/1(0.525M NaCl)60/1 (0.6M NaCl)60/1 Fine tuning – never observed before! Less diluent solvating power = more phase separation

11 Effect of morphology on swelling

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13 Effect of morphology on equilibrium shear modulus

14 PCA: 35 water-born samples, 19 variables

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17 PCA: 35 samples, 4 variables Equilibrium swelling, low frequency modulus, and pair of loss factors These variables are important as such, and therefore they are usually determined

18 Conclusions and perspectives PCA approach is promising for indirect morphology assessment. Fairly reliable Fast and cheap as compared with the direct ESEM Uses experimental variables are important as such Needs further investigation Is it possible to exclude swelling data? Creep curve fitting? Does the approach work with chemically different materials?


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