PMID- 16316107
OWN - NLM
STAT- PubMed-not-MEDLINE
DCOM- 20150521
LR  - 20051130
IS  - 1520-5827 (Electronic)
IS  - 0743-7463 (Linking)
VI  - 21
IP  - 25
DP  - 2005 Dec 6
TI  - Hydrophobization of glass surface by adsorption of poly(dimethylsiloxane).
PG  - 11729-37
AB  - Silica or glass particles are introduced in a poly(dimethylsiloxane) (PDMS) 
      matrix for various applications. A particular feature of these systems is that 
      PDMS adsorbs on the surface of the dispersed particles, thus rendering them more 
      hydrophobic with time. The mechanism of this process of in situ hydrophobization 
      is still poorly understood. The major aims of the present study are (1) to 
      quantify the rate of surface hydrophobization by PDMS and, on this basis, to 
      discuss the mechanism of the process; (2) to compare the contact angles of 
      surfaces that are hydrophobized by different procedures and are placed in contact 
      with different fluid interfaces-PDMS-water, hexadecane-water, and air-water; and 
      (3) to check how the type of surfactant affects the contact angles, viz., the 
      effective hydrophobicity of the surface. We present experimental results for the 
      kinetics of hydrophobization of glass surfaces, which are characterized by 
      measuring the three-phase contact angle of glass-surfactant solution-PDMS. The 
      data reveal two consecutive stages in the hydrophobization process: The first 
      stage is relatively fast and the contact angle increases from 0 degrees to about 
      90 degrees within several minutes. This stage is explained with the physical 
      adsorption of the PDMS chains, as a result of hydrogen-bond formation with the 
      surface silanol groups. The second stage is much slower and hours or days are 
      required at room temperature to reach the final contact angle (typically, 150-160 
      degrees). This stage is explained as grafting of the PDMS molecules on the 
      surface by chemical reaction with the surface silanol groups. If the glass 
      surface had been pretreated by hexamethyldisilazane (HMDS), so that CH(3) groups 
      had blocked most of the surface silanol groups, the first stage in the 
      hydrophobization process is almost missing-the contact angle slowly changes at 
      room temperature from about 90 degrees up to 120 degrees. The experiments aimed 
      to compare several hydrophobization procedures showed that PDMS ensures larger 
      contact angle (more hydrophobic surface) than grafted alkyl chains. The contact 
      angles at the PDMS-water and hexadecane-water interfaces were found to be very 
      similar to each other, and much larger than that at the air-water interface. 
      Interestingly, we found that the ionic surfactants practically do not affect the 
      contact angle of PDMS-hydrophobized surface, whereas the nonionic surfactants 
      reduce this angle. Similar trends are expected with silica surfaces, as well.
FAU - Marinova, Krastanka G
AU  - Marinova KG
AD  - Laboratory of Chemical Physics & Engineering, Faculty of Chemistry, Sofia 
      University, Bulgaria.
FAU - Christova, Diana
AU  - Christova D
FAU - Tcholakova, Slavka
AU  - Tcholakova S
FAU - Efremov, Evtim
AU  - Efremov E
FAU - Denkov, Nikolai D
AU  - Denkov ND
LA  - eng
PT  - Journal Article
PL  - United States
TA  - Langmuir
JT  - Langmuir : the ACS journal of surfaces and colloids
JID - 9882736
EDAT- 2005/12/01 09:00
MHDA- 2005/12/01 09:01
CRDT- 2005/12/01 09:00
PHST- 2005/12/01 09:00 [pubmed]
PHST- 2005/12/01 09:01 [medline]
PHST- 2005/12/01 09:00 [entrez]
AID - 10.1021/la051690t [doi]
PST - ppublish
SO  - Langmuir. 2005 Dec 6;21(25):11729-37. doi: 10.1021/la051690t.