porosity characterzation in soft matter · 2012. 11. 29. · polymer precipitation/freeze drying...

Porosity Analysis in Soft Microporous Matter Jens Weber

Max Planck Institute of Colloids and Interfaces, Department of Colloid Chemistry, Science Park Golm 1, D-14424 Potsdamhttp://www.mpikg.mpg.de/kolloidchemie/arbGruppen/PorousPolymers/index.html; jens.weber@mpikg.mpg.de

Acknowledgements: Markus Antonietti, Bernd Smarsly, Matthias Thommes, Antje Wilke, Jekaterina Jeromenok, Miriam Unterlass , Pablo Haro Dominguez, Antonio Stocco, Arne Thomas, Marlies Gräwert, Ingrid Zenke, Irina Shekova, Chez Briel crowd

linear microporousPolymers

(non-cross-linked)

Microporous Polymers• found interest in gas separation/storage; catalysis applications

• can be synthesized by a large number of ways• are: amorphous, light weight and chemically stable

but:their porosity is far less understood (compared to inorganics)

Intrinsically Microporous Polymersare based on hindered packing of contorted, stiff polymers

(ultra-high free volume is obtained and accessible = measurable microporosity)

linear polyimides(Nicola Ritter)

H2 sorption at 77.3K revealed the presence of microporosity for almost

all materials (precipitated) However: still some unusual isotherms

(strong hysteresis upon desorption)

H2 sorption: Irena Senkovska, Stefan Kaskel (TU Dresden)

carbon dioxide sorption at 273K:

all materials adsorb CO2 –even in the solvent cast state

(no H2 adsorption for cast films!)

solubility effects? temperature effect?

microporousPolymer networks

(highly cross-linked)

Conclusionswhen analyzing microporous polymers one has to pay attention to:

Analysis Temperature Processing History Intra/Intermolecular Interactions

Polymeric structures exhibit significantdifferences in mobility at 77K and 273K, respectively

Impact on pore accessibility

Polymer precipitation/freeze drying can yield metastable statesdifference to film casting/evaporative drying Impact on pore accessibility and size

Interactions (e.g. hydrogen-bonding) can close poresof soft porous matter! switchable porosity

Selected References: Macromolecules 2008, 41, 2880-2885, Macromol. Rapid Commun. 2007, 28, 1871-1876; J. Am. Chem. Soc. 2008, 130, 6334-6335; Adv. Mater. 2009, 21, 702-705; Macromolecules. 2009, 42, 8017-8020; Langmuir2010, 26, 15650-15656; Macromol. Rapid Commun. 2011, 32, 438-443; Macromolecules 2011, 44, 2025-2033; Macromolecules 2011, 44, 1763-1767, J. Mater Chem. 2011, 21, 5226-5229

129Xe-NMR: Winfried Böhlmann (Uni Leipzig)

Rpore ~ 0.36 nm

SpPAT network: Johannes Schmidt, Arne Thomas (TU Berlin)

Preliminary experiments show that solubility could most probable be ruled out!(no significant difference in adsorption enthalpy betweendifferently processed samples)Influence of polymer chain dynamics at the different measurement temperatures seems more important(see scheme below)

initial N2 and Ar sorption on precipitated samples showed no porosity or obscure

isotherms (swelling/gating etc.)

crosslinking provides stable porositybut:

• significant hysteresis upon desorption• pronounced swelling

impact on determination of porosityparameters (pore volume, PSD)?

significant swelling is observed! (note: different slopes for N2 and Ar, stronger swellingin N2) – In the case of strong swelling (SpPAT), a significant mismatch between thedifferent DFT kernels is observed. For SpPI, a better agreement is observed, but N2alone cannot resolve the average pore size – CO2 sorption and/or 129Xe NMR areneeded. The observed pore sizes are smaller than expected. different scenarios are possible: = spirobifluorene, = linker

ideal Interdigitated deformed / reversibly collapsed

stiff andconotorted chains