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In spite of making a small contribution to total protoplanetary disk mass,dust affects the disk temperature by controlling absorption of starlight. Asgrains grow from their initial ISM-like size distribution, settling depletesthe disk's upper layers of dust and decreases the optical depth, cooling theinterior. Here we investigate the effect of collisional growth of dust grainsand their dynamics on the thermal and optical profile of the disk, and explorethe possibility that cooling induced by grain growth and settling could lead togravitational instability. We develop a Monte Carlo dust collision model with aweighting technique and allow particles to collisionally evolve throughsticking and fragmentation, along with vertical settling and turbulent mixing.We explore two disk models, the MMEN (minimum-mass extrasolar nebula), and a"heavy" disk with higher surface density than the MMEN, and perform simulationsfor both constant and spatially variable turbulence efficiency profile$\alpha(R,z)$. We then calculate mean wavelength-dependent opacities for theevolving disks and perform radiative transfer to calculate the temperatureprofile $T(R,z)$. Finally, we calculate the Toomre Q parameter, a measure ofthe disk's stability against self-gravity, for each disk model after it reachesa steady state dust-size distribution. We find that even weak turbulence cankeep sub-micron sized particles stirred in the disk's upper layer, affectingits optical and thermal profiles, and the growth of large particles in themidplane can make a massive disk optically thick at millimeter wavelengths,making it difficult to calculate the surface density of dust available forplanet formation in the inner disk. Also, for an initially massive disk, grainsettling and growth can produce a drop in the Toomre Q parameter, driving thedisk to $Q < 1.4$ and possibly triggering spiral instabilities.

Dust Growth and Dynamics in Protoplanetary Nebulae: Implications for Opacity, Thermal Profile and Gravitational Instability