Langmuir deposition

Next, the sensitivity of this technique to extremely small refractive index changes will also be demonstrated in light of ultrathin photochromic layers self-assembled on glass substrates, but first we discuss the self-assembly and Langmuir deposition techniques. 

Evans S.D., Sanassy P. and Uhnan A. 1994. Mixed alkanethiolate monolayers as substrates for studying the Langmuir deposition process. Thin Sohd Films, 243, 325-329. 

We have not considered here alignment techniques, such as SiOx deposition or alignement by monolayer (Langmuir) deposition on surfaces. Details on these techniques of surface alignment can be found elsewhere [5-9]. We also do not discuss recently introduced active (command) surfaces, where the anchoring conditions are controlled by light [55], electrochemistry [56] and electric field [57]. 

Let s now investigate the last mechanistic point, namely the kinetic features of deposition. The S-type of the deposition isotherm achieved in all cases suggested Langmuir deposition with lateral attractive interactions between the deposited species. A typical example is illustrated in fig. 13. 

In this chapter, we discuss the Langmuir deposition of ultrathin PDA fihns and the subsequent measurement of their structural, optical, and mechanical properties at the nanometer scale. By altering the head group functionality, we can choose between mono- and tri-layer PDA film structures. We then show that we can use the tip of an atomic force microscope (AFM) or a near field scanning optical microscope (NSOM) tip to locally convert the PDA from the blue form to the red form via applied stress. This represents the first time that mechanochromism has been observed at the nanometer scale. Dramatic structural changes are associated with this mechanochromic transition. 

We have produced high-quality ultrathin PDA films using a horizontal Langmuir deposition technique. The number of stable layers in die film is controlled by altering the head group functionality. The films exhibit strong fiiction anisotropy that is correlated with the directiop of the polymer backbone... 

A belief that solid interfaces are easier to understand than liquid ones shifted emphasis to the former but the subjects are not really separable, and the advances in the one are giving impetus to the other. There is increasing interest in films of biological and of liquid crystalline materials because of the importance of thin films in microcircuitry (computer chips ), there has been in recent years a surge of activity in the study of deposited mono- and multilayers. These Langmuir-Blodgett films are discussed in Section XV-7. 

Langmuir-Blodgett flint deposited on copper. From graphic integration of the data of Ref. 144. See Ref. 158. 

Films spread at liquid-liquid interfaces or on liquids other than water are discussed followed by the important effects of charged monolayers on water. Finally, the most technologically important application of Langmuir films, the Langmuir-Blodgett film deposited on a solid substrate, is reviewed. 

Other interesting Langmuir monolayer systems include spread thermotropic liquid crystals where a foam structure forms on expansion from a collapsed state [23]. Spread monolayers of clay dispersions form a layer of overlapping clay platelets that can be subsequently deposited onto solid substrates [24]. 

The transfer of Langmuir films from the air-liquid surface to a solid substrate has come to be known as Langmuir-Blodgett deposition, after its developers [130, 131]. The solid substrates are usually hydrophilic surfaces such as... 

Deposited Langmuir-Blodgett films take on many of the same stmctures as the Langmuir monolayers discussed in Section IV-4C, and they are often compared to the self-assembling monolayers described in Section XI-IB. The area... 

From what you know about wetting, contact angles, and spread monolayers, explain why a Langmuir-Blodgett layer will deposit as a F type if there are nonpolar fatty acids, yet will switch to a Z-type deposition if bipolar alcohols or amines are added (see Refs. 175, 176). What defines the critical contact angle for the deposition change ... 

Roberts C J, Williams P M, Davies J, Dawkes A C, Sefton J, Edwards J C, Haymes A G, Bestwick C, Davies M C and Tendler S J B 1995 Real-space differentiation of IgG and IgM antibodies deposited on microtiter wells by scanning force microscopy Langmuir 1822... 

Tredgold R FI, Jones S D, Evans S D and Williams P I 1986 Aluminium oxide as a substrate for the deposition of Langmuir-Blodgett films J. Mol. Electron. 2 147-9... 

Peterson I R, Veale G and Montgomery C M 1986 The preparation of oleophilio surfaoes for Langmuir-Blodgett deposition J. Colloid Interface Sc/. 109 527-30... 

Mayva K S ef a/1998 On the deposition of Langmuir-Blodgett films of Q-state CdS nanopartioles through eleotrostatio immobilization at the air-water interfaoe Thin Solid Films 2M 300... 

Langmuir-Blodgett films (LB) and self assembled monolayers (SAM) deposited on metal surfaces have been studied by SERS spectroscopy in several investigations. For example, mono- and bilayers of phospholipids and cholesterol deposited on a rutile prism with a silver coating have been analyzed in contact with water. The study showed that in these models of biological membranes the second layer modified the fluidity of the first monolayer, and revealed the conformation of the polar head close to the silver [4.300]. 

Figure 5.21. Experimental setup (inset) showing the location of the working (WE), counter (CE) and reference (RE) electrodes and of the heating element (HE) thermal desorption spectra after gaseous oxygen dosing at 673 K and an 02 pressure of 4x1 O 6 Torr on Pt deposited on YSZ for various exposure times. Oxygen exposure is expressed in kilo-langmuirs (1 kL=l0 3 Torrs). Desorption was performed with linear heating rate, ()=1 K/s.4 S Reprinted with permission from Academic Press.

This precipitation process can be carried out rather cleverly on the surface of a reverse phase. If the protein solution is brought into contact with a reversed phase, and the protein has dispersive groups that allow dispersive interactions with the bonded phase, a layer of protein will be adsorbed onto the surface. This is similar to the adsorption of a long chain alcohol on the surface of a reverse phase according to the Langmuir Adsorption Isotherm which has been discussed in an earlier chapter. Now the surface will be covered by a relatively small amount of protein. If, however, the salt concentration is now increased, then the protein already on the surface acts as deposition or seeding sites for the rest of the protein. Removal of the reverse phase will separate the protein from the bulk matrix and the original protein can be recovered from the reverse phase by a separate procedure. 

Dominguez, D.D.,Mowery, R. L., and Turner, N. H., Friction and Durabilities of Well-Ordered, Close Packed Carboxylic Acid Monolayers Deposited on Glass and Steel Surfaces by the Langmuir-Blodgett Technique, Tribal. Trans., yi. No. 1, 1994, pp. 59-66. 

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