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Temperature responsive surface layers of modified celluloses
KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
2011 (Engelska)Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 10, s. 4260-4268Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The temperature-dependent properties of pre-adsorbed layers of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) were investigated on silica and hydrophobized silica surfaces. Three different techniques, quartz crystal microbalance with dissipation monitoring, ellipsometry, and atomic force microscopy imaging, were used, providing complementary and concise information on the structure, mass and viscoelastic properties of the polymer layer. Adsorption was conducted at 25 degrees C, followed by a rinsing step. The properties of such pre-adsorbed layers were determined as a function of temperature in the range 25 degrees C to 50 degrees C. It was found that the layers became more compact with increasing temperature and that this effect was reversible, when decreasing the temperature. The compaction was more prominent for MC, as shown in the AFM images and in the thickness data derived from the QCM analysis. This is consistent with the fact that the phase transition temperature is lower, in the vicinity of 50 degrees C, for MC than for HPMC. The water content of the adsorbed layers was found to be high, even at the highest temperature, 50 degrees C, explored in this investigation.

Ort, förlag, år, upplaga, sidor
2011. Vol. 13, nr 10, s. 4260-4268
Nyckelord [en]
QUARTZ-CRYSTAL MICROBALANCE, ETHYL HYDROXYETHYL CELLULOSE, AQUEOUS-SOLUTIONS, THERMAL GELATION, HYDROXYPROPYL METHYLCELLULOSE, VISCOELASTIC PROPERTIES, OPTICAL-PROPERTIES, IONIC SURFACTANT, DEPENDENT FORCES, POLYMER LAYERS
Nationell ämneskategori
Kemi
Identifikatorer
URN: urn:nbn:se:kth:diva-31311DOI: 10.1039/c0cp02074eISI: 000287584700010PubMedID: 21246125Scopus ID: 2-s2.0-79951941383OAI: oai:DiVA.org:kth-31311DiVA, id: diva2:404830
Forskningsfinansiär
Vetenskapsrådet
Anmärkning
QC 20110318Tillgänglig från: 2011-03-18 Skapad: 2011-03-14 Senast uppdaterad: 2020-03-09Bibliografiskt granskad
Ingår i avhandling
1. Bulk and interfacial properties of cellulose ethers
Öppna denna publikation i ny flik eller fönster >>Bulk and interfacial properties of cellulose ethers
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This work summarizes several studies that all concern cellulose ethers of the types methylcellulose (MC) hydroxypropylmethylcellulose (HPMC) and ethyl(hydroxyethyl)cellulose (EHEC). They share the feature of negative temperature response, as they are soluble in water at room temperature but phase separate and sometimes form gels at high temperatures. The different types of viscosity transitions occurring in these three cellulose ethers are well-known. However, earlier studies have not solved the problem of why both HPMC and EHEC, as the temperature increases, exhibit a viscosity decrease just before the viscosity increases, whereas MC only has one transition temperature where the viscosity increases. With our investigations we have aimed to compare the effect of temperature on bulk solutions and on adsorbed layers of the different polymers using a range of techniques.

Light scattering and cryo transmission electron microscopy (cryo-TEM) was employed to study aggregation of MC, HPMC and EHEC in solution. The solvent quality of water is reduced for all three polymers in solution as the temperature increases, and this infers an onset of aggregation at a certain temperature. The aggregation rate follows the order EHEC > HPMC > MC. Cryo-TEM pictures of solutions frozen from high temperatures showed closely packed fibrils forming dense networks in MC solution. Some fibrils were also found in HPMC solution above the transition temperature, but they did not interconnect readily. This is explained by the bulky and hydrophilic hydroxypropyl groups attached to HPMC. EHEC has similar substituents, while MC only has short and hydrophobic methyl groups attached to the main chain.

An amphiphilic liquid, diethyleneglycolmonobutylether (BDG) was used as an additive to change the properties of MC solutions in water. With 10 wt% BDG added, the effect was similar in viscosity and light scattering measurements as well as cryo-TEM pictures, inducing a temperature response resembling that of HPMC in pure water. 5 wt% of BDG was enough to change the aggregation type and induce a transition temperature with viscosity decrease. The effect of the additive is rationalized by BDG acting as a hydrophobic and bulky substituent in MC, similar to the large substituents in HPMC and EHEC.

Two instruments, a quartz crystal microbalance with dissipation (QCM-D) and an ellipsometer, were used in parallel to determine the changes with temperature on an adsorbed layer of MC and HPMC on silica kept in water and in polymer solution. The silica needed to be hydrophobized for significant adsorption to take place. Adsorption was similar for both polymers at low temperatures, whereas a sharp transition in several layer properties occurred for HPMC, but not for MC, close to the solution viscosity transition temperature. Atomic force microscopy (AFM) was used to measure attractive and repulsive forces and also friction forces between MC layers in polymer solution. The small changes in normal forces with temperature infer that the hydrophobic groups in MC are mostly depleted from the surface. The surface–polymer interactions increase with increasing temperature and the layer becomes more cohesive, which induces a higher load bearing capacity and lower friction when measured at high loads. AFM imaging was employed to obtain the height distribution in MC adsorbed layers. These images indicate that fibril-like structures were formed at a lower temperature in the surface layer than in bulk solution.

The different preferences for adsorption and for aggregation in MC and HPMC above the solution transition temperatures are explained by the fibril formation in MC shielding hydrophobic parts of the polymer from the solution, and thus counteracting adsorption, but also fast aggregation. The viscosity decrease in HPMC and EHEC is conferred to intra-chain contraction and aggregation into less extended structures.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2012. s. 41
Serie
Trita-CHE-Report, ISSN 1654-1081 ; 2012:22
Nationell ämneskategori
Fysikalisk kemi
Identifikatorer
urn:nbn:se:kth:diva-95379 (URN)978-91-7501-347-3 (ISBN)
Disputation
2012-06-01, D3, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20120523

Tillgänglig från: 2012-05-23 Skapad: 2012-05-23 Senast uppdaterad: 2012-09-25Bibliografiskt granskad

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